Cell conversion into cochlear hair cells

Abstract

The present disclosure relates to compositions and methods for the conversion of source cells (such as cochlear support cells) to cochlea hair cells and / or cochlea hair cell-like cells by introducing transcription factors (TFs) into the source cells, and methods for treating hearing loss.

Description

[0001] CELL CONVERSION INTO COCHLEAR HAIR CELLS

[0002] Technical field

[0003] The present disclosure relates to compositions and methods for the conversion of source cells (such as cochlear support cells) to cochlea hair cells and / or cochlea hair cell-like cells by introducing transcription factors (TFs) into the source cells, and methods for treating hearing loss.

[0004] Background to the invention

[0005] Cochlear hair cells (inner and outer) are located in the inner ear. Their function involves sensing sound and transmitting the signal to auditory neurons. The death of cochlear hair cells, for example due to ageing, noise damage or ototoxic drugs, results in hearing loss since sensory cells in the mammalian cochlea are unable to proliferate after birth. Sensorineural hearing loss, which involves the inner ear, accounts for about 90% of all cases of hearing loss. An estimated 1.57 billion people globally had hearing loss in 2019, accounting for one in five people.

[0006] The feasibility of reprogramming a variety of source mammalian cells to cochlear hair cells using transcription factors has been previously investigated. Existing approaches have consistently focussed on the transcription factor Atoh1 , which has been accepted as essential for cochlear hair cell development for decades (for example, in reference to Math1, the mouse homology of AT0H1, Bermingham et al MathT. An Essential Gene for the Generation of Inner Ear Hair Cells. Science 284,1837-1841 (1999)). Unsurprisingly, therefore, the potential use of Atoh1 to regenerate sensory hair cells and treat hearing loss has long been recognised, see for example W02004 / 076626 and Izumikawa et al., Nature Medicine 2005, 11 , 271-276. Accordingly, in 2014 Novartis began a clinical trial (NCT02132130) to evaluate the safety, tolerability, and the potential ability of CGF166 delivered through IL-infusion to improve hearing. CGF166 is a recombinant adenovirus 5 (Ad5) vector containing a cDNA encoding the human Atonal transcription factor ( “HATH1 ”, now known as ATOH1). The clinical trial reported that CGF166 was safe and well tolerated. However, the primary objective of the study was not met as there was no or minimal improvement in pure tone audiometry (air conduction) compared to pretreatment values; only 2 subjects (9.1%) showed meaningful improvement in hearing loss at select frequences after being tested. It was therefore concluded that CGF166 did not result in a clinically meaningful improvement.

[0007] Importantly, these results have not been interpreted by the field as necessitating a move away from Atoh1 . In contrast, the long history of the Atoh1 paradigm of cochlea hair cell reprogramming has led to a technical prejudice in the field that Atoh1 should be supplemented, rather than replaced. For instance, even before the results of NCT02132130 were published, it was stated in WO2018 / 148071 “the FDA has approved a clinical trial (NCT02132130) for assessing safety, tolerability and efficacy of CGF166, a recombinant adenovirus 5 (Ad5) vector containing a cDNA encoding the human Atoh1 . However, it is not clear whether Atoh1 -mediated non-sensory supporting cell-to-sensory hair cell conversion in vivo is efficient and complete and whether such conversion bypasses the progenitor-cell state or follows normal developmental lineage paths precisely. Therefore, the identify of additional factors to improve efficiency and completion are needed.” The need to supplement, rather replace Atohl for the clinical application of cochlear hair cell reprogramming is widely held by researchers and clinicians in the field. As a further example, a textbook chapter entitled ‘Approaches to Regenerate Hair Cell and Spiral Ganglion Neuron in the Inner Ear” by Waqas and Chai published in the book titled “New Therapies to Prevent or Cure Auditory Disorders” (2020) describes only one transcription factor-based approach to regenerate cochlear hair cells; in a section entitled “2.3 Atohl-Based Gene Therapy” the textbook describes how the “first human clinical trial for hearing restoration “CGF166” is still underway since 2014. The preliminary findings regarding the effectiveness and feasibility of Atohl gene in humans are unpublished yet” and also describes a number of transcription factors which may be used in combination with Atohl . This technical prejudice to supplementing Atohl is has since been strengthened by clinical trial results concerning CGF166 showing Atohl to be safe and well tolerated, but clinically ineffective when delivered alone.

[0008] Before the CGF166 clinical trial began, a study reported that permanent Atohl expression in endogenous hair cells of genetically engineered mice induced cell loss of mature hair cells (Liu et a / (2012) 32(19):6600- 6610). The same study concluded that “taken together, our data suggest that a combination of Atohl expression with other factors is needed to convert PCs [pillar cells] and DCs [Deiters’ cells] (especially at adult ages) into fully differentiated, functional HCs [hair cells]”.

[0009] Indeed, this technical prejudice to supplementing Atohl is has since been strengthened by multiple studies over more than a decade that have demonstrated that supplementing Atohl can improve hair cell regeneration relative to Atohl alone. Early work attempted supplementing ATOH1 with TFE2 and GATA3 (Masuda et al Dev. Biol. 372 (2012) 68-80. Subsequent work attempted supplementing ATOH1 with Gfi1 and Pou4f3 (Costa et al. 2015 Development 142, 1948-1959). The field of transcription factor-based reprogramming in the inner ear was recently reviewed (Iyer & Groves 2021 Front. Cell. Neurosci. 15:660748). The authors describe the findings of several research groups working within the Atohl paradigm of cochlea hair cell reprogramming. These are summarised under the heading “Hair Cell Reprogramming Strategies Employing Atohl in Combination With Other Reprogramming Partners”. Key citations represented in Figure 2 of Iyer & Groves (2021) are identified and briefly described below:

[0010] • Costa etal. 2015 Development 142, 1948-1959 describes in vitro experiments aiming to reprogram chick otic epithelium and mouse embryonic stem (ES) cells towards a hair cell fate using Atohl in combination with Gfi1 and Pou4f3.

[0011] • Walters et al. 2017 Cell Rep. 19(2): 307-320 describes in vivo experiments aiming to reprogram adult supporting cells towards hair cells using Atohl in combination with Pou4f3, Gata3 and / or deletion of p27.

[0012] • Yamashita et al. 2018 PLoS Genet. 14:e1007552 (see also WO2018 / 148071) describes in vitro and in vivo experiments aiming to reprogram cells towards hair cells using Atohl in combination with Isl1 .

[0013] • Lee et al. 2020 Sci. Rep. 10:21397 describes in vitro and in vivo experiments aiming to reprogram cells towards hair cells using Atohl in combination with Gfi1 .

[0014] • Menendez et al. 2020 eLife 2020;9:e55249 describes in vitro experiments aiming to reprogram cells towards hair cells using Atohl in combination with Gfi1 , Pou4f3 and Six1 . Notably, Menendez et al. 2020 assessed the effect of 16 TFs (in combination and separately), including Atohl , Gfi1 , Pou4f3, Six1 and Lhx3, and observed that only Atohl alone (and none of the 15 other TFs tested individually) led to a reporter activation greater than that achieved by the 16 TFs in combination. Furthermore, the authors note even the “induced hair cells” made using Atohl in combination with Gfi1 , Pou4f3 and Six1 “fail to activate other important genes essential for the functional maturation of the sensory receptors in the cochlea, such as Prestin”.

[0015] In a further recent review (Rai et al. Int. J. Mol. Sci. 2022, 23, 66), the authors noted that Atohl has been described as “the master regulator of HC [hair cell] differentiation and regeneration”. They also suggest “modulating multiple TFs in combination with Atohl is a good strategy to promote regeneration and increase the number of regenerated HCs”. The combination of Gfi1 , Pou4f3 and Atohl (“GPA”) currently stands out as consistently showing improved cell conversion relative to Atohl alone by multiple research groups in numerous systems (Costa et al. (2015); Walters et al. (2017); Menendez et al. (2020); Chen et al., 2021 , Cell Reports 35, 109016; lyer et al. 2022 eLife 11 :e79712).

[0016] Before and since the conclusion of NCT02132130, researchers in the field have overwhelmingly pursued cochlear hair cell regeneration strategies using combinatorial approaches using Atohl in combination with other reprogramming factors. However, there remains an unmet clinical need to provide means for cochlear hair cell reprogramming which provide efficient cell reprogramming, a clinically viable number of reprogrammed hair cells and an increased functional maturity of reprogrammed hair cells while reducing any loss of mature hair cells. It is an object of the present invention to address one or more of these problems.

[0017] Summary of the invention

[0018] The present inventors have surprisingly identified approaches to cochlear hair cell reprogramming that do not require Atohl . Circumventing transcription factors that are not required for cell reprogramming may lead to technical advantages. These include maximising the available cargo space in a chosen delivery vehicle and the avoidance of potential gene expression problems. Each exogenous transcription factor to be delivered takes up cargo space in a chosen delivery vehicle. Pushing the limits of cargo space may impair the expression of the transcription factors delivered and limit effective production of the chosen delivery vehicle. Delivering more transcription factors may increase the number of vectors required, which may in turn reduce therapeutic efficacy because only a subset of cells may receive and express all of the transcription factors delivered by multiple vehicles. These related problems are particularly acute when transcription factors are delivered by vehicles with a comparatively small cargo capacity, such as adeno- associated virus (AAV), which has a maximum cargo capacity lower than alternative viral vectors such as lentivirus and adenovirus. Maximising the available cargo space in a chosen delivery vehicle and / or avoiding gene expression problems by omitting inessential transcription factors may in turn allow improvements in efficacy. For instance, if it is not necessary to use cargo capacity on a particular transcription factor, then this frees up cargo capacity to use for another purpose, such as the delivery of an alternative transcription factor which may improve cell conversion. Accordingly, approaches to cochlear hair cell reprogramming that surprisingly do not require Atohl may improve the deliverability and / or efficacy of therapies for hearing loss. Further, as exemplified herein, the present inventors have surprisingly found that approaches to cochlear hair cell reprogramming that do not require Atohl can provide further advantages compared with conventional approaches using Atohl , such as increasing the number of cochlear hair cells produced, increasing the proportion of mature cochlear hair cells produced, and reducing cochlear hair cell loss. Thus, approaches to cochlear hair cell reprogramming that surprisingly do not require Atohl may further provide cochlear hair cells with improved clinical utility compared with conventional Atohl -based approaches.

[0019] The present inventors have demonstrated these benefits in mouse cochlear explants (ex vivo), in vivo mouse models, and human cell lines. Specifically, in mouse models, reprogramming without Atohl has been shown to result in a higher number of cochlear hair cells, including a greater proportion of mature, functional cells, as well as a reduction in hair cell loss. Similarly, in human cell lines, the Atohl-independent approach has resulted in enhanced activation of genes associated with the hair cell phenotype, and a specific synergistic effect on key regulators of hair cell identity. These findings suggest that Atohl- independent reprogramming may provide a more effective and durable strategy for cochlear hair cell regeneration, with potential to improve clinical outcomes.

[0020] According to a first aspect, the invention provides a nucleic acid molecule encoding at least two transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the nucleic acid molecule does not encode Atohl .

[0021] According to a second aspect, the invention provides a system for increasing expression of genes encoding at least two transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

[0022] According to a third aspect, the invention provides a vector comprising the nucleic acid molecule according to the first aspect or the system comprising one or more nucleic acid molecules according to the second aspect.

[0023] According to a fourth aspect, the invention provides a composition comprising the nucleic acid molecule according to the first aspect, the system comprising one or more nucleic acid molecules according to the second aspect or the vector according to the third aspect, and a pharmaceutically acceptable carrier.

[0024] According to a fifth aspect, the invention provides a product comprising

[0025] (a) a first nucleic acid molecule, encoding at least one transcription factor, or a functional variant thereof, selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, and

[0026] (b) a second nucleic acid molecule, encoding at least one transcription factor, or a functional variant thereof, selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3; wherein the first nucleic acid molecule and the second nucleic acid molecule each encode different transcription factors and wherein the product does not comprise a nucleic acid molecule encoding Atohl ; as a combined preparation for simultaneous, separate or sequential use in the treatment of hearing loss.

[0027] According to a sixth aspect, the invention provides a product comprising

[0028] (a) a first nucleic acid molecule, configured to target for upregulation at least one transcription factor, or a functional variant thereof, selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3, and

[0029] (b) a second nucleic acid molecule, configured to target for upregulation at least one transcription factor, or a functional variant thereof, selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3; wherein the first nucleic acid molecule and the second nucleic acid molecule are each configured to target for upregulation different transcription factors and wherein the product does not comprise a nucleic acid molecule configured to target Atohl for upregulation; as a combined preparation for simultaneous, separate or sequential use in the treatment of hearing loss.

[0030] According to a seventh aspect, the invention provides a kit for introducing and / or increasing the protein expression of at least two transcription factors, or functional variants thereof, in a source cell, wherein the at least two transcription factors are selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

[0031] According to an eighth aspect, the invention provides a method of converting a source cell to a target cell by introducing and / or increasing the protein expression of at least two transcription factors, or functional variants thereof, into the source cell, thereby converting the source cell into the target cell, wherein the at least two transcription factors are selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

[0032] According to a ninth aspect, the invention provides a cell produced by the method of the eighth aspect.

[0033] According to a tenth aspect, the invention provides the nucleic acid molecule according to the first aspect, the system comprising one or more nucleic acid molecules according to the second aspect, the vector according to the third aspect, the composition according to the fourth aspect, the kit according to the seventh aspect, or the cell according to the ninth aspect for use in the treatment of hearing loss.

[0034] According to an eleventh aspect, the invention provides a method of treating hearing loss in a subject in need thereof comprising administering to the subject a therapeutically effective amount of the nucleic acid molecule according to the first aspect, the system comprising one or more nucleic acid molecules according to the second aspect, the vector according to the third aspect, the composition according to the fourth aspect, the product according to the fifth aspect, the product according to the sixth aspect, the kit according to the seventh aspect, or the cell according to the ninth aspect. Any of the features described herein in respect of any of the above-mentioned aspects of the invention may be combined mutatis mutandis with the other aspects of the invention.

[0035] Brief description of the drawings

[0036] Figure 1 . Mogrify TF combinations increase the cell count of Myo7a expression in Sox2+ cells in neonatal explants in vitro. Images of the middle and basal areas of the organ of Corti were acquired using confocal microscopy (Zeiss LSM700, 20x). Cells in the supporting cell layer of the hair cell region were quantified for each area. Myo7a+ Sox2+ positive cells were calculated as a fraction of the total Sox2+ cells in each image. Total Myo7a intensity was measured for double positive cells.

[0037] Figure 2. Map of the AAV transfer plasmid vector used for the manufacture of AAV used in the present Examples to deliver Gfi1 and Pou4f3. Used in the following conditions: Gfi1 and Pou4f3 (GP), Gfi1 , Pou4f3 and Atohl (GPA), Gfi1 , Pou4f3, Lhx3 and Six2 (GPLS), Gfi1 , Pou4f3, Isl1 and Kcnip3 (GPIK), Gfi1 , Pou4f3, Pknox2 and Kcnip3 (GPPK).

[0038] Figure 3. Map of the AAV transfer plasmid vector used for the manufacture of AAV used in the present Examples to deliver Lhx3 and Six2. Used in Gfi1 , Pou4f3, Lhx3 and Six2 (GPLS).

[0039] Figure 4. Map of the AAV transfer plasmid vector used for the manufacture of AAV used in the present Examples to deliver Isl1 and Kcnip3. Used in Gfi1 , Pou4f3, Isl1 and Kcnip3 (GPIK).

[0040] Figure 5. Map of the AAV transfer plasmid vector used for the manufacture of AAV used in the present Examples to deliver Pknox2 and Kcnip3. Used in Gfi1 , Pou4f3, Isl1 and Kcnip3 (GPIK), Gfi1 , Pou4f3, Pknox2 and Kcnip3 (GPPK).

[0041] Figure 6. Map of the AAV transfer plasmid vector used for the manufacture of AAV used in the present Examples to deliver Atohl . Used in Atohl and Gfi1 , Pou4f3 and Atohl (GPA).

[0042] Figure 7. Map of the AAV transfer plasmid vector used for the manufacture of AAV used in the present Examples to deliver eGFP. Used as a control.

[0043] Figure 8. GPAand Atohl both induce large numbers of P1 -like immature hair cells which are largely absent in cells treated with Gfi1 , Pou4f3, Lhx3 and Six2 (GPLS), Gfi1 , Pou4f3, Isl1 and Kcnip3 (GPIK), or GfH , Pou4f3, Pknox2 and Kcnip3 (GPPK). UMAP representations of the cells isolated from each sample with P1-like hair cells indicated in grey.

[0044] Figure 9. All three TF combinations (Gfi1 , Pou4f3, Lhx3 and Six2 (GPLS), Gfi1 , Pou4f3, Isl1 and Kcnip3 (GPIK), and Gfi1 , Pou4f3, Pknox2 and Kcnip3 (GPPK)) cause Prestin to be expressed in significantly more supporting cells than the eGFP control. Bar charts represent counts of supporting cells that yield any Prestin transcript sequencing reads. Error bars are bootstrapped 95% confidence intervals. Figure 10. All three of Gfi1 , Pou4f3, Lhx3 and Six2 (GPLS), Gfi1 , Pou4f3, Isl1 and Kcnip3 (GPIK), and Gfi1 , Pou4f3, Pknox2 and Kcnip3 (GPPK)elevate the expression levels of Prestin in at least two of the Prestin-positive cell populations, as compared to Atohl or GPA controls. Gfi1 , Pou4f3, Lhx3 and Six2 (GPLS), Gfi1 , Pou4f3, Isl1 and Kcnip3 (GPIK), and Gfi1 , Pou4f3, Pknox2 and Kcnip3 (GPPK)all elevate the expression levels of Prestin relative to eGFP. Box plots show the median and interquartile range of expression within cells identified as expressing the Prestin gene above background levels.

[0045] Figure 11 . Atohl and Gfi1 , Pou4f3 and Atohl (GPA) induce trajectories towards indeterminate Pllike hair cell and inner hair cell phenotypes. UMAP representations of supporting and hair cell populations isolated from each sample, with computed RNA velocity trajectories overlaid as arrows. Large numbers of P1-like hair cells are induced and show clear trajectories towards an endpoint situated between the mature inner and outer hair cell clusters, with GPA promoting further transition towards the mature IHC cluster. Grey shading represents new-to-total RNA ratios (ntr), a measure of RNA splicing activity (i.e., the fraction of RNA present in each cell which has been spliced). The levels of unspliced RNAs provide an indication of expected future levels of the fully-functional spliced RNA for each gene, and so the ratios of spliced to unspliced RNAs can be used to compute a velocity (direction plus magnitude) of cell phenotype change.

[0046] Figure 12. Gfi1 , Pou4f3, Lhx3 and Six2 (GPLS), Gfi1 , Pou4f3, Isl1 and Kcnip3 (GPIK), and Gfi1 , Pou4f3, Pknox2 and Kcnip3 (GPPK) induce greater movement towards the mature outer hair cell phenotype. UMAP representations of supporting and hair cell populations isolated from each sample, with computed RNA velocity trajectories overlaid as arrows. Transitioning cells are induced in relatively low numbers and show trajectories oriented towards outer hair cells. Grey shading represents new-to-total RNA ratios (ntr), a measure of RNA splicing activity (i.e., the fraction of RNA present in each cell which has been spliced). The levels of unspliced RNAs provide an indication of expected future levels of the fully-functional spliced RNA for each gene, and so the ratios of spliced to unspliced RNAs can be used to compute a velocity (direction plus magnitude) of cell phenotype change.

[0047] Figure 13. Gfi1 , Pou4f3, Pknox2 and Kcnip3 (GPPK) induces a cell trajectory from supporting cells to hair cells. FDL projection overlaid with arrows indicating RNA velocity. The addition of the Gfi 1 , Pou4f3, Pknox2 and Kcnip3 (GPPK) TF combination induces a bridging trajectory of intermediate cells between the supporting cell populations (top right) and the mature hair cells (bottom left). This intermediate cell trajectory is absent in the eGFP control.

[0048] Figure 14. FDL projection overlaid with arrows indicating RNA velocity. The supporting cell to hair cell observed for the Gfi1 , Pou4f3, Pknox2 and Kcnip3 (GPPK) combination is not directly observed in samples treated with control TFs (Atohl or Gfi1 , Pou4f3 and Atohl (GPA)) or the other Mogrify TF combinations (Gfi1 , Pou4f3, Lhx3 and Six2 (GPLS), Gfi1 , Pou4f3, Isl1 and Kcnip3 (GPIK)). In both Gfi1 , Pou4f3, Lhx3 and Six2 (GPLS) and Gfi1 , Pou4f3, Isl1 and Kcnip3 (GPIK), however, we detect an early population of potentially transitioning cells (indicated) that is absent in both Atohl and Gfi1 , Pou4f3 and Atohl (GPA) samples.

[0049] Figure 15. Preliminary data suggest Mogrify TF combinations induce cell conversion events in vivo. Representative images of cells transduced with the indicated Mogrify TF combinations and stained with Sox2, Myo7a and 2A peptide antibodies. White arrows indicate the location of triple positive (Sox2+ Myo7a+ 2A+) cells. These cells may represent Mogrify TF expressing cells in the process of undergoing conversion.

[0050] Figure 16. Mogrify TF combinations have lower toxicity towards inner hair cells (IHC) than Atohl and Gfi1 , Pou4f3 and Atohl (GPA). It is notable that Gfi1 , Pou4f3 and Atohl (GPA) causes significantly more IHC loss than Atohl alone. However, all three of Gfi1 , Pou4f3, Lhx3 and Six2 (GPLS), Gfi1 , Pou4f3, Isl1 and Kcnip3 (GPIK), and Gfi1 , Pou4f3, Pknox2 and Kcnip3 (GPPK) show strikingly reduced IHC loss relative to Gfi1 , Pou4f3 and Atohl (GPA). Hair cell survival was assessed by visual observation and categorized as ‘lost,’ ‘partial’ or ‘remaining’ as indicated in the figure legend. Significance was calculated using Fisher’s Exact test with two degrees of freedom.

[0051] Figure 17. Significant synergy between transcription factors in upregulating cochlear hair cell signature genes in human cells was observed. Differential expression scores are calculated as described in Example 7. For the set of cochlear hair cell marker genes, their differential expression scores were averaged and calculated the standard error. Additionally, it was tested whether these are significantly upregulated from any random set of genes of the same size using a permutation test (1 ,000 random sets of genes of the same size as the original, n=1 ,037 genes). As observed, the transcription factor combination Gfi1 and Pou4f3 (GP) has the largest effect on upregulating cochlear hair cell signature genes. Surprisingly, the addition of Atohl to Gfi1 and Pou4f3 (GPA) does not induce further upregulation of cochlear hair cell signature genes. Addition of Six2 or Lhx3 to Gfi 1 also shows upregulation of cochlear hair cell signature genes.

[0052] Detailed description

[0053] According to a first aspect, the invention provides a nucleic acid molecule encoding at least two transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the nucleic acid molecule does not encode Atohl .

[0054] The data disclosed herein are derived from delivery of at least two transcription factors selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, without including Atohl . The combinations tested were compared to Atohl alone and / or Gfi1 , Pou4f3 and Atohl (GPA). Immunofluorescence data indicate the ability of combinations to generate hair cells (both mature and immature) and for example surprisingly show Pou4f3 and Gfi1 without Atohl perform similarly to GPA while generating a greater number of hair cells than Atohl alone. Moreover, sequencing data highlight combinations without Atohl that show improved signs of a mature hair cell phenotype relative to those achieved by Atohl alone or by GPA. Atohl alone and GPA each generates a substantial population of “P1- like” immature hair cells, which is not observed in the combinations omitting Atohl , which instead produce populations showing signs of a more mature hair cell phenotype. Expression of Atohl in adult mice in vivo is shown herein to lead to a partial loss of inner hair cells, an effect which is exacerbated by the addition of Pou4f3 and Gfi1 alongside Atohl . Surprisingly, three transcription factor combinations that include Pou4f3 and Gfi1 but not Atohl are shown to significantly reduce the inner hair cell loss caused by GPA expression. Delivery of at least two transcription factors selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3, without delivering Atohl , may represent advantageous combinations of transcription factors for cochlear hair cell reprogramming and in treatments for hearing loss.

[0055] The nucleic acid molecule may comprise a nucleic acid sequence encoding at least two transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the nucleic acid molecule does not encode Atohl .

[0056] The nucleic acid molecule may comprise at least two of:

[0057] (a) a nucleic acid sequence encoding Pou4f3 or a functional variant thereof,

[0058] (b) a nucleic acid sequence encoding Gfi1 or a functional variant thereof,

[0059] (c) a nucleic acid sequence encoding Lhx3 or a functional variant thereof,

[0060] (d) a nucleic acid sequence encoding Isl1 or a functional variant thereof,

[0061] (e) a nucleic acid sequence encoding Six2 or a functional variant thereof,

[0062] (f) a nucleic acid sequence encoding Pknox2 or a functional variant thereof,

[0063] (g) a nucleic acid sequence encoding Kcnip3 or a functional variant thereof,

[0064] Wherein the nucleic acid molecule does not comprise a nucleic acid sequence encoding Atohl or a functional variant thereof.

[0065] It is not excluded that the nucleic acid molecule may encode one or more additional transcription factor not selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. For example, in the context of a polycistronic expression vector the nucleic acid molecule may encode one or more additional transcription factor not selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. However, the one or more additional transcription factor encoded by the nucleic acid molecule may not include Atohl . The nucleic acid molecule may not encode Atohl . The nucleic acid molecule may not comprise a nucleic acid sequence encoding Atohl or a functional variant thereof.

[0066] The nucleic acid molecule may encode at least one transcription factor and at least one functional variant of a different transcription factor. The nucleic acid molecule may encode at least one transcription factor selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3 and at least one functional variant of a different transcription factor selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. The nucleic acid molecule may encode at least one transcription factor selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, at least one functional variant of a different transcription factor selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, and may not encode Atohl . The nucleic acid molecule may encode at least one transcription factor selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, at least one functional variant of a different transcription factor selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, and may not encode a functional variant of Atohl .

[0067] The nucleic acid molecule may comprise at least two of:

[0068] (a) a nucleic acid sequence encoding Pou4f3,

[0069] (b) a nucleic acid sequence encoding Gfi1 ,

[0070] (c) a nucleic acid sequence encoding Lhx3,

[0071] (d) a nucleic acid sequence encoding Isl1 ,

[0072] (e) a nucleic acid sequence encoding Six2,

[0073] (f) a nucleic acid sequence encoding Pknox2,

[0074] (g) a nucleic acid sequence encoding Kcnip3,

[0075] Wherein the nucleic acid molecule does not comprise a nucleic acid sequence encoding Atohl .

[0076] According to any aspect of the invention, the transcription factors may comprise at least two of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3 or a functional variant of any thereof. The transcription factors may comprise at least one functional variant. For example, the transcription factors may comprise a functional variant of Pou4f3 and at least one other transcription factor selected from the group consisting of Gfi1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3 or a functional variant of any thereof. The transcription factors may comprise a functional variant of Gfi1 and at least one other transcription factor selected from the group consisting of Pou4f3, Lhx3, Isl1 , Six2, Pknox2 and Kcnip3 or a functional variant of any thereof. The transcription factors may comprise a functional variant of Lhx3 and at least one other transcription factor selected from the group consisting of Pou4f3, Gfi 1 , Isl1 , Six2, Pknox2 and Kcnip3 or a functional variant of any thereof. The transcription factors may comprise a functional variant of Isl1 and at least one other transcription factor selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Six2, Pknox2 and Kcnip3 or a functional variant of any thereof. The transcription factors may comprise a functional variant of Six2 and at least one other transcription factor selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl 1 , Pknox2 and Kcnip3 or a functional variant of any thereof. The transcription factors may comprise a functional variant of Pknox2 and at least one other transcription factor selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, and Kcnip3 or a functional variant of any thereof. The transcription factors may comprise a functional variant of Kcnip3 and at least one other transcription factor selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2 and Pknox2 or a functional variant of any thereof. The transcription factors may comprise at least two functional variants. The transcription factors may comprise at least three functional variants. The transcription factors may comprise at least four functional variants. According to any aspect of the invention, the transcription factors may comprise at least two of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3.

[0077] As used herein, “Pou4f3” refers to POU class 4 homeobox transcription factor 3. In humans it is encoded by the POU4F3 gene, also known as BRN3C, DFNA15, DFNA42 and DFNA52. The mouse ortholog Pou4f3 is also known as ddl; Brn3c; Brn3.1 and dreidel. In humans, the Ensembl gene ID is ENSG00000091010. An example of a transcript is the Ensembl transcript ID ENST00000646991 .2 and the UniProt ID is Q15319; codon-optimised and alternatively spliced transcript variants are encompassed. In mice, the Ensembl gene ID is ENSMUSG00000024497. An example of a transcript is the Ensembl transcript ID ENST00000646991 .2 and the UniProt ID is Q63955; codon-optimised and alternatively spliced transcript variants are encompassed. A synergy between Pou4f3 and Atohl has been previously reported, for example by Menendez et al. (2020), where Pou4f3 had little or no effect alone but significantly enhanced the effect of Atohl .

[0078] Pou4f3 may refer to the human sequence having the following amino acid sequence, identified as SEQ ID NO: 1

[0079] SEQ ID NO: 1

[0080] MMAMNSKQPFGMHPVLQEPKFSSLHSGSEAMRRVCLPAPQLQGNIFGSFDESLLARAEALAAVDIVSHG KNHPFKPDATYHTMSSVPCTSTSSTVPISHPAALTSHPHHAVHQGLEGDLLEHISPTLSVSGLGAPEHSV MPAQIHPHHLGAMGHLHQAMGMSHPHTVAPHSAMPACLSDVESDPRELEAFAERFKQRRIKLGVTQAD VGAALANLKIPGVGSLSQSTICRFESLTLSHNNMIALKPVLQAWLEEAEAAYREKNSKPELFNGSERKRKR TSIAAPEKRSLEAYFAIQPRPSSEKIAAIAEKLDLKKNWRVWFCNQRQKQKRMKYSAVH

[0081] Pou4f3 may refer to the mouse sequence having the following amino acid sequence, identified as SEQ ID NO: 2

[0082] SEQ ID NO: 2

[0083] MMAMNAKQPFGMHPVLQEPKFSSLHSGSEAMRRVCLPAPQLQGNIFGSFDESLLARAEALAAVDIVSHG KNHPFKPDATYHTMSSVPCTSTSPTVPISHPAALTSHPHHAVHQGLEGDLLEHISPTLSVSGLGAPEHSV MPAQIHPHHLGAMGHLHQAMGMSHPHAVAPHSAMPACLSDVESDPRELEAFAERFKQRRIKLGVTQADV GAALANLKIPGVGSLSQSTICRFESLTLSHNNMIALKPVLQAWLEEAEAAYREKNSKPELFNGSERKRKRT SIAAPEKRSLEAYFAIQPRPSSEKIAAIAEKLDLKKNWRVWFCNQRQKQKRMKYSAVH

[0084] Pou4f3 may be encoded by the following human coding sequence, identified as SEQ ID NO: 3

[0085] SEQ ID NO: 3

[0086] ATGATGGCCATGAACTCCAAGCAGCCTTTCGGCATGCACCCGGTGCTGCAAGAACCCAAATTCTCCA GTCTGCACTCTGGCTCCGAGGCCATGCGCCGAGTCTGTCTCCCAGCCCCGCAGCTGCAGGGTAATA TATTTGGAAGCTTTGATGAGAGCCTGCTGGCACGCGCCGAAGCTCTGGCGGCGGTGGATATCGTCTC CCACGGCAAGAACCATCCGTTCAAGCCCGACGCCACCTACCATACCATGAGCAGCGTGCCCTGCAC GTCCACTTCGTCCACCGTGCCCATCTCCCACCCAGCTGCGCTCACCTCACACCCTCACCACGCCGT GCACCAGGGCCTCGAAGGCGACCTGCTGGAGCACATCTCGCCCACGCTGAGTGTGAGCGGCCTGG GCGCTCCGGAACACTCGGTGATGCCCGCACAGATCCATCCACACCACCTGGGCGCCATGGGCCACC TGCACCAGGCCATGGGCATGAGTCACCCGCACACCGTGGCCCCTCATAGCGCCATGCCTGCATGCC TCAGCGACGTGGAGTCAGACCCGCGCGAGCTGGAAGCCTTCGCCGAGCGCTTCAAGCAGCGGCGC ATCAAGCTGGGGGTGACCCAGGCGGACGTGGGCGCGGCTCTGGCTAATCTCAAGATCCCCGGCGT GGGCTCGCTGAGCCAAAGCACCATCTGCAGGTTCGAGTCTCTCACTCTCTCGCACAACAACATGATC GCTCTCAAGCCGGTGCTCCAGGCCTGGTTGGAGGAGGCCGAGGCCGCCTACCGAGAGAAGAACAG CAAGCCAGAGCTCTTCAACGGCAGCGAACGGAAGCGCAAACGCACGTCCATCGCGGCGCCGGAGA AGCGTTCACTCGAGGCCTATTTCGCTATCCAGCCACGTCCTTCATCTGAGAAGATCGCGGCCATCGC TGAGAAACTGGACCTTAAAAAGAACGTGGTGAGAGTCTGGTTCTGCAACCAGAGACAGAAACAGAAA

[0087] CGAATGAAGTATTCGGCTGTCCACTGA

[0088] Pou4f3 may be encoded by the following mouse coding sequence, identified as SEQ ID NO: 4

[0089] SEQ ID NO: 4

[0090] ATGATGGCCATGAACGCCAAGCAGCCTTTCGGCATGCACCCCGTACTGCAAGAACCCAAATTCTCCA

[0091] GCCTACACTCCGGCTCTGAGGCCATGCGCCGAGTTTGTCTCCCAGCCCCGCAGCTGCAGGGTAATA

[0092] TATTTGGAAGCTTTGATGAGAGCCTGCTGGCACGCGCCGAAGCTCTGGCGGCGGTGGATATCGTCTC

[0093] CCACGGCAAGAATCATCCGTTCAAGCCCGACGCCACCTACCATACCATGAGCAGCGTGCCCTGCACT

[0094] TCTACCTCGCCCACGGTGCCCATCTCTCACCCGGCTGCACTCACCTCGCACCCGCATCACGCGGTA

[0095] CATCAGGGCCTCGAGGGCGACTTACTTGAGCACATCTCGCCCACGCTGAGCGTGAGTGGCCTAGGG

[0096] GCCCCGGAGCACTCGGTGATGCCGGCGCAGATCCACCCGCATCATCTAGGCGCCATGGGCCACTTG

[0097] CATCAGGCCATGGGCATGAGTCACCCGCATGCCGTAGCACCGCACAGTGCCATGCCCGCGTGTCTC

[0098] AGCGATGTGGAGTCAGACCCTCGAGAGCTGGAAGCGTTCGCCGAGCGCTTCAAGCAGAGGCGCAT

[0099] CAAGTTGGGGGTCACCCAGGCGGACGTGGGCGCGGCTTTAGCCAATCTTAAGATCCCCGGTGTGGG

[0100] CTCGCTCAGCCAGAGCACCATCTGCAGGTTCGAGTCTCTTACTCTGTCGCACAACAACATGATCGCT

[0101] CTCAAGCCGGTCCTCCAGGCCTGGCTGGAGGAGGCCGAGGCCGCCTACCGAGAGAAGAACAGCAA

[0102] GCCAGAGCTCTTCAACGGCAGTGAGCGTAAGCGCAAACGCACGTCCATCGCCGCGCCAGAGAAGC

[0103] GCTCACTCGAAGCCTATTTCGCCATCCAGCCACGTCCTTCATCCGAGAAGATCGCGGCCATCGCGGA

[0104] GAAACTGGACCTTAAAAAGAATGTGGTGAGGGTCTGGTTCTGTAACCAGAGACAGAAACAGAAACGA

[0105] ATGAAATACTCTGCTGTCCACTGA

[0106] Pou4f3 may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 5

[0107] SEQ ID NO: 5

[0108] ATGATGGCCATGAATGCTAAGCAGCCTTTTGGCATGCACCCCGTGCTCCAGGAGCCAAAGTTCTCCA

[0109] GCCTGCACTCCGGCTCCGAAGCTATGAGAAGGGTGTGTCTGCCAGCTCCACAGCTCCAGGGAAACA

[0110] TCTTCGGAAGCTTCGACGAAAGCCTGCTCGCACGGGCTGAGGCTCTGGCCGCTGTGGACATCGTAT

[0111] CCCACGGTAAGAACCACCCATTTAAGCCAGACGCTACCTATCATACAATGTCTTCCGTGCCATGCACA

[0112] AGCACCTCTCCCACCGTGCCTATAAGCCATCCAGCCGCTCTGACCTCTCACCCCCACCACGCCGTGC

[0113] ATCAGGGCCTGGAAGGAGATCTCCTGGAACACATCAGTCCTACCCTGTCCGTGTCCGGCCTCGGCG

[0114] CTCCTGAACACAGCGTGATGCCTGCCCAAATTCACCCACACCACCTGGGCGCCATGGGCCACCTGC

[0115] ACCAGGCTATGGGCATGAGCCATCCTCACGCTGTGGCCCCTCACAGTGCAATGCCAGCCTGTCTCTC

[0116] CGACGTGGAGAGCGACCCCAGGGAGCTGGAGGCCTTCGCCGAGAGATTCAAGCAGAGAAGAATCA

[0117] AGCTCGGCGTGACACAGGCCGACGTGGGCGCCGCCCTGGCCAATCTGAAGATCCCTGGCGTGGGC

[0118] TCACTGAGCCAGTCCACAATCTGTAGGTTCGAAAGTCTGACTCTGAGCCACAACAACATGATCGCCC

[0119] TCAAACCCGTGCTCCAGGCATGGCTGGAGGAAGCCGAGGCCGCCTATCGAGAGAAGAACTCTAAGC

[0120] CTGAACTGTTTAATGGCAGCGAGAGAAAGAGAAAGAGAACCAGCATCGCCGCCCCTGAAAAGCGTT

[0121] CCCTGGAGGCTTACTTTGCCATCCAGCCACGACCCTCCAGCGAGAAGATCGCCGCCATCGCCGAAA

[0122] AGCTTGACCTGAAGAAGAACGTGGTGAGGGTATGGTTCTGTAACCAGAGACAGAAGCAGAAGAGGAT

[0123] GAAGTACAGCGCAGTGCACTGA Pou4f3 may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 57

[0124] SEQ ID NO: 57

[0125] ATGATGGCCATGAACGCCAAGCAGCCCTTCGGCATGCATCCCGTGCTGCAAGAGCCTAAGTTCAGCA GCCTGCACTCTGGCAGCGAGGCCATGAGAAGAGTGTGTCTGCCTGCTCCTCAGCTGCAGGGCAACA TCTTCGGCAGCTTCGACGAGTCTCTGCTGGCCAGAGCTGAAGCACTGGCCGCTGTGGATATCGTGT CCCACGGCAAGAATCACCCCTTCAAGCCTGACGCCACCTACCACACAATGAGCAGCGTGCCATGCA CCAGCACAAGCCCTACCGTGCCTATCTCTCACCCTGCCGCTCTGACATCTCACCCTCACCACGCTGT GCACCAGGGACTTGAAGGCGATCTGCTGGAACACATCAGCCCCACACTGTCCGTGTCTGGACTGGG CGCTCCTGAGCATTCTGTGATGCCCGCTCAGATCCATCCTCACCACCTGGGCGCTATGGGACATCTG CATCAGGCCATGGGCATGTCTCACCCACATGCTGTGGCTCCCCACTCTGCCATGCCTGCTTGTCTGA GCGACGTGGAAAGCGACCCCAGAGAGCTGGAAGCCTTCGCCGAGAGATTCAAGCAGAGAAGAATCA AGCTGGGCGTGACCCAGGCCGATGTTGGAGCTGCTCTGGCTAACCTGAAGATCCCTGGCGTGGGCA GCCTGAGCCAGTCTACCATCTGTAGATTCGAGAGCCTGACACTGAGCCACAACAACATGATCGCCCT GAAGCCTGTGCTGCAGGCCTGGCTGGAAGAAGCTGAGGCTGCCTACAGAGAGAAGAACAGCAAGC CCGAGCTGTTCAACGGCAGCGAGCGCAAGAGAAAGAGAACCTCTATCGCTGCCCCTGAGAAGAGAA GCCTGGAAGCTTACTTCGCCATCCAGCCTAGACCTAGCAGCGAGAAGATCGCCGCTATCGCCGAGAA GCTGGACCTGAAGAAAAACGTCGTCAGAGTGTGGTTCTGCAACCAGCGGCAGAAACAGAAACGGAT GAAGTACAGCGCCGTGCACTGA

[0126] The functional variant of Pou4f3 may comprise an amino acid sequence at least 70% identical to SEQ ID NO: 1 or SEQ ID NO: 2. The functional variant of Pou4f3 may comprise an amino acid sequence at least 80% identical to SEQ ID NO: 1 or SEQ ID NO: 2. The functional variant of Pou4f3 may comprise an amino acid sequence at least 85% identical to SEQ ID NO: 1 or SEQ ID NO: 2. The functional variant of Pou4f3 may comprise an amino acid sequence at least 90% identical to SEQ ID NO: 1 or SEQ ID NO: 2. The functional variant of Pou4f3 may comprise an amino acid sequence at least 95% identical to SEQ ID NO: 1 or SEQ ID NO: 2. The functional variant of Pou4f3 may comprise an amino acid sequence at least 96% identical to SEQ ID NO: 1 or SEQ ID NO: 2. The functional variant of Pou4f3 may comprise an amino acid sequence at least 97% identical to SEQ ID NO: 1 or SEQ ID NO: 2. The functional variant of Pou4f3 may comprise an amino acid sequence at least 98% identical to SEQ ID NO: 1 or SEQ ID NO: 2. The functional variant of Pou4f3 may comprise an amino acid sequence at least 99% identical to SEQ ID NO: 1 or SEQ ID NO: 2. SEQ ID NO: 1 and SEQ ID NO: 2 share 335 identical amino acids out of 338 and thus are at least 99% identical to one another. The nucleic acid sequence may comprise any nucleic acid sequence encoding a functional variant of Pou4f3. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 70% identical to SEQ ID NO: 1 or SEQ ID NO: 2. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 90% identical to SEQ ID NO: 1 or SEQ ID NO: 2. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 99% identical to SEQ ID NO: 1 or SEQ ID NO: 2. The functional variant of Pou4f3 may consist essentially of an amino acid sequence at least 70% identical to SEQ ID NO: 1 or SEQ ID NO: 2. The functional variant of Pou4f3 may consist essentially of any amino acid sequence described elsewhere herein as a sequence that the functional variant of Pou4f3 may comprise.

[0127] The nucleic acid sequence may comprise any nucleic acid sequence encoding Pou4f3. Pou4f3 may comprise an amino acid sequence according to SEQ ID NO: 1 or SEQ ID NO: 2. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 1 or SEQ ID NO: 2. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 1 . Alternatively, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 2.

[0128] The nucleotide sequence encoding Pou4f3 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0129] (a) SEQ ID NO: 1 ,

[0130] (b) SEQ ID NO: 2,

[0131] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 1 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 1 , or

[0132] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 2 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 2.

[0133] The nucleotide sequence encoding Pou4f3 or a functional variant thereof may consist essentially of a nucleic acid sequence encoding:

[0134] (a) SEQ ID NO: 1 ,

[0135] (b) SEQ ID NO: 2,

[0136] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 1 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 1 , or

[0137] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 2 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 2.

[0138] The nucleotide sequence encoding Pou4f3 or a functional variant thereof may consist essentially of any nucleic acid sequence described elsewhere herein as a sequence that may encode Pou4f3 or functional variant of Pou4f3.

[0139] The nucleotide sequence encoding Pou4f3 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0140] (a) SEQ ID NO: 1 ,

[0141] (b) SEQ ID NO: 2,

[0142] (c) an amino acid sequence having at least 99% identify to SEQ ID NO: 1 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 1 , or

[0143] (d) an amino acid sequence having at least 99% identify to SEQ ID NO: 2 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 2. The nucleotide sequence encoding Pou4f3 or a functional variant thereof may comprise:

[0144] (a) SEQ ID NO: 3,

[0145] (b) SEQ ID NO: 4,

[0146] (c) SEQ ID NO: 5,

[0147] (d) SEQ ID NO: 57, or

[0148] (d) a nucleotide sequence having at least 60% identity to SEQ ID NO: 3, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 1 , or

[0149] (e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 4, SEQ ID NO: 5, or SEQ ID NO: 57 wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 2.

[0150] The nucleotide sequence encoding Pou4f3 or a functional variant thereof may comprise a nucleic acid sequence having at least 60% identity to SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5 or SEQ ID NO: 57. The nucleotide sequence having at least 60% identity to SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5 or SEQ ID NO: 57 may have at least 70%, 75%, 80%, 85%, 90% or 95% identity to SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5 or SEQ ID NO: 57, respectively. SEQ ID NO: 3 and SEQ ID NO: 4 share 931 identical nucleotides out of 1017 and thus are at least 91 % identical to one another. SEQ ID NO: 4 and SEQ ID NO: 5 share 794 identical nucleotides out of 1017 and therefore have at least 78% sequence identity to each other and encode the same protein sequence. SEQ ID NO: 4 and SEQ ID NO: 57 share 797 identical nucleotides out of 1017 and therefore have at least 78% sequence identity to each other and encode the same protein sequence. The non-identical nucleotides may represent silent mutations (i.e. mutations which do not alter the sequence of the encoded amino acid). The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid, for example by one or more conservative amino acid mutation. The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid by up to 20, up to 15, up to 10, up to 9, up to 8, up to 7, up to 6, up to 5, up to 4, up to 3, up to 2 or up to 1 conservative amino acid mutation.

[0151] The nucleotide sequence encoding Pou4f3 or a functional variant thereof may comprise:

[0152] (a) SEQ ID NO: 3,

[0153] (b) SEQ ID NO: 4,

[0154] (c) SEQ ID NO: 5,

[0155] (d) SEQ ID NO: 57, or

[0156] (d) a nucleotide sequence having at least 78% identity to SEQ ID NO: 3, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 1 , or

[0157] (e) a nucleotide sequence having at least 78% identity to SEQ ID NO: 4, SEQ ID NO: 5 or SEQ ID NO: 57, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 2.

[0158] The nucleotide sequence encoding Pou4f3 or a functional variant thereof may comprise:

[0159] (a) SEQ ID NO: 3,

[0160] (b) SEQ ID NO: 4,

[0161] (c) SEQ ID NO: 5, (d) SEQ ID NO: 57 or

[0162] (d) a nucleotide sequence having at least 91 % identity to SEQ ID NO: 3, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 1 , or

[0163] (e) a nucleotide sequence having at least 91 % identity to SEQ ID NO: 4 ,SEQ ID NO: 5 or SEQ ID NO: 57, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 2.

[0164] The nucleic acid sequence may encode Pou4f3. The nucleotide sequence encoding Pou4f3 may comprise:

[0165] (a) SEQ ID NO: 3,

[0166] (b) SEQ ID NO: 4,

[0167] (c) SEQ ID NO: 5, or

[0168] (d) SEQ ID NO: 57.

[0169] The nucleic acid molecule may encode at least two transcription factors, or functional variants thereof, wherein one transcription factor is Pou4f3 and wherein the at least two transcription factors further comprise at least one transcription factor selected from the group consisting of Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

[0170] According to any aspect of the invention, the transcription factors may comprise:

[0171] (a) Pou4f3 and Gfi1 ;

[0172] (b) Pou4f3 and Lhx3

[0173] (c) Pou4f3 and Isl1 ;

[0174] (d) Pou4f3 and Six2

[0175] (e) Pou4f3 and Pknox2; or

[0176] (f) Pou4f3 and Kcnip3.

[0177] According to any aspect of the invention, the transcription factors may comprise:

[0178] (a) Pou4f3, Gfi1 and Lhx3

[0179] (b) Pou4f3, Gfi1 and Isl1 ;

[0180] (c) Pou4f3, Gfi1 and Six2

[0181] (d) Pou4f3, Gfi1 and Pknox2; or

[0182] (e) Pou4f3, Gfi1 and Kcnip3.

[0183] As used herein, “Gfi1 ” refers to growth factor independent 1 transcription repressor. In humans it is encoded by the GFI1 gene, also known as GFI-1 , GFI1A, SCN2 and ZNF163. The mouse ortholog Gfi1 is also known as Pall , Gfi-1 and Pal-1. In humans, the Ensembl gene ID is ENSG00000162676. An example of a transcript is the Ensembl transcript ID ENST00000370332.5 and the UniProt ID is Q99684; codon- optimised and alternatively spliced transcript variants are encompassed. In mice, the Ensembl gene ID is ENSMUSG00000029275. An example of a transcript is the Ensembl transcript ID ENSMUST00000031205.16 and the UniProt ID is A0A0R4J292; codon-optimised and alternatively spliced transcript variants are encompassed. A synergy between Gfi1 and the combination of Atohl and Pou4f3 has been previously reported, for example by Menendez et al. (2020), where Gfi1 had no effect alone and failed to enhance the effect of Atohl , but significantly enhanced the combined effect of Atohl and Pou4f3.

[0184] Gfi1 may refer to the human sequence having the following amino acid sequence, identified as SEQ ID NO: 6

[0185] SEQ ID NO: 6

[0186] MPRSFLVKSKKAHSYHQPRSPGPDYSLRLENVPAPSRADSTSNAGGAKAEPRDRLSPESQLTEAPDRAS

[0187] ASPDSCEGSVCERSSEFEDFWRPPSPSASPASEKSMCPSLDEAQPFPLPFKPYSWSGLAGSDLRHLVQ

[0188] SYRPCGALERGAGLGLFCEPAPEPGHPAALYGPKRAAGGAGAGAPGSCSAGAGATAGPGLGLYGDFGS

[0189] AAAGLYERPTAAAGLLYPERGHGLHADKGAGVKVESELLCTRLLLGGGSYKCIKCSKVFSTPHGLEVHVR RSHSGTRPFACEMCGKTFGHAVSLEQHKAVHSQERSFDCKICGKSFKRSSTLSTHLLIHSDTRPYPCQYC GKRFHQKSDMKKHTFIHTGEKPHKCQVCGKAFSQSSNLITHSRKHTGFKPFGCDLCGKGFQRKVDLRR

[0190] HRETQHGLK

[0191] Gfi1 may refer to the mouse sequence having the following amino acid sequence, identified as SEQ ID NO: 7

[0192] SEQ ID NO: 7

[0193] MPRSFLVKSKKAHSYHQPRSPGPDYSLRLETVPAPGRAEGGAVSAGESKMEPRERLSPDSQLTEAPDR

[0194] ASASPNSCEGSVCDPCSEFEDFWRPPSPSVSPASEKSLCRSLDEAQPYTLPFKPYAWSGLAGSDLRHLV QSYRQCSALERSAGLSLFCERGSEPGRPAARYGPEQAAGGAGAGQPGSCGVAGGATSAAGLGLYGDF APAAAGLYERPSTAAGRLYQDHGHELHADKSVGVKVESELLCTRLLLGGGSYKCIKCSKVFSTPHGLEVH

[0195] VRRSHSGTRPFACEMCGKTFGHAVSLEQHKAVHSQERSFDCKICGKSFKRSSTLSTHLLIHSDTRPYPCQ YCGKRFHQKSDMKKHTFIHTGEKPHKCQVCGKAFSQSSNLITHSRKHTGFKPFGCDLCGKGFQRKVDL RRHRETQHGLK

[0196] Gfi1 may be encoded by the following human coding sequence, identified as SEQ ID NO: 8

[0197] SEQ ID NO: 8

[0198] ATGCCGCGCTCATTTCTCGTCAAAAGCAAGAAGGCTCACAGCTACCACCAGCCGCGCTCCCCAGGA

[0199] CCAGACTATTCCCTCCGTTTAGAGAATGTACCGGCGCCTAGCCGAGCAGACAGCACTTCAAATGCAG

[0200] GCGGGGCGAAGGCGGAGCCCCGGGACCGTTTGTCCCCCGAATCGCAGCTGACCGAAGCCCCAGA

[0201] CAGAGCCTCCGCATCCCCAGACAGCTGCGAAGGCAGCGTCTGCGAACGGAGCTCGGAGTTTGAGG

[0202] ACTTCTGGAGGCCCCCGTCACCCTCCGCGTCTCCAGCCTCGGAGAAGTCAATGTGCCCATCGCTGG

[0203] ACGAAGCCCAGCCCTTCCCCCTGCCTTTCAAACCGTACTCATGGAGCGGCCTGGCGGGTTCTGACC

[0204] TGCGGCACCTGGTGCAGAGCTACCGACCGTGTGGGGCCCTGGAGCGTGGCGCTGGCCTGGGCCT

[0205] CTTCTGCGAACCCGCCCCGGAGCCTGGCCACCCGGCCGCGCTGTACGGCCCGAAGCGGGCTGCC

[0206] GGCGGCGCGGGGGCCGGGGCGCCAGGGAGCTGCAGCGCAGGGGCCGGTGCCACCGCTGGCCCT

[0207] GGCCTAGGGCTCTACGGCGACTTCGGGTCTGCGGCAGCCGGGCTGTATGAGAGGCCCACGGCAGC

[0208] GGCGGGCTTGCTGTACCCCGAGCGTGGCCACGGGCTGCACGCAGACAAGGGCGCTGGCGTCAAG

[0209] GTGGAGTCGGAGCTGCTGTGCACCCGCCTGCTGCTGGGCGGCGGCTCCTACAAGTGCATCAAGTG CAGCAAGGTGTTCTCCACGCCGCACGGGCTCGAGGTGCACGTGCGCAGGTCCCACAGCGGTACCA

[0210] GACCCTTTGCCTGCGAGATGTGCGGCAAGACCTTCGGGCACGCGGTGAGCCTGGAGCAGCACAAA

[0211] GCCGTGCACTCGCAGGAACGGAGCTTTGACTGTAAGATCTGTGGGAAGAGCTTCAAGAGGTCATCC

[0212] ACACTGTCCACACACCTGCTTATCCACTCAGACACTCGGCCCTACCCCTGTCAGTACTGTGGCAAGA

[0213] GGTTCCACCAGAAGTCAGACATGAAGAAACACACTTTCATCCACACTGGTGAGAAGCCTCACAAGTG

[0214] CCAGGTGTGCGGCAAGGCATTCAGCCAGAGCTCCAACCTCATCACCCACAGCCGCAAACACACAGG

[0215] CTTCAAGCCCTTCGGCTGCGACCTCTGTGGGAAGGGTTTCCAGAGGAAGGTGGACCTCCGAAGGCA

[0216] CCGGGAGACGCAGCATGGGCTCAAATGA

[0217] Gfi1 may be encoded by the following mouse coding sequence, identified as SEQ ID NO: 9

[0218] SEQ ID NO: 9

[0219] ATGCCGCGCTCATTCCTGGTCAAGAGCAAGAAGGCGCACAGCTATCACCAGCCGCGTTCTCCGGGG

[0220] CCGGACTACTCCCTGCGCCTGGAGACCGTGCCTGCGCCGGGCAGAGCAGAGGGCGGCGCTGTGA

[0221] GTGCAGGCGAGTCGAAAATGGAGCCCCGAGAGCGTTTGTCCCCCGACTCTCAGCTTACCGAGGCTC

[0222] CCGACAGGGCCTCCGCGTCCCCCAACAGCTGCGAAGGCAGCGTTTGTGACCCCTGCTCCGAGTTC

[0223] GAGGACTTTTGGAGGCCCCCTTCTCCCTCCGTGTCTCCAGCGTCGGAGAAGTCACTGTGCCGCTCT

[0224] CTGGACGAAGCCCAGCCCTACACGCTGCCTTTCAAGCCCTATGCATGGAGCGGTCTTGCTGGGTCT

[0225] GACCTGCGGCACCTGGTGCAGAGCTATCGGCAGTGCAGCGCGCTGGAGCGCAGCGCGGGCCTGA

[0226] GCCTCTTCTGCGAGCGCGGCTCGGAGCCGGGCCGCCCGGCAGCGCGCTACGGCCCCGAGCAGGC

[0227] TGCGGGCGGAGCCGGTGCGGGACAGCCAGGGAGCTGCGGGGTCGCCGGGGGCGCCACCAGCGC

[0228] TGCGGGCCTGGGGCTCTACGGCGACTTCGCGCCTGCGGCGGCCGGGCTGTACGAGCGGCCGAGC

[0229] ACAGCAGCAGGCCGGCTGTACCAAGATCATGGCCACGAGCTGCACGCGGACAAGAGCGTGGGCGT

[0230] CAAGGTGGAGTCGGAGCTGCTTTGCACCCGTCTGCTGCTGGGCGGCGGCTCCTACAAATGCATCAA

[0231] ATGCAGCAAGGTGTTCTCCACACCGCACGGGCTGGAGGTGCACGTGCGCCGGTCCCACAGCGGCA

[0232] CAAGACCCTTTGCGTGCGAGATGTGCGGCAAGACCTTCGGGCACGCGGTGAGCCTGGAGCAACAC

[0233] AAGGCAGTGCACTCCCAGGAACGCAGCTTTGACTGTAAGATCTGTGGCAAGAGCTTCAAGAGGTCAT

[0234] CCACGCTGTCCACACATCTGCTCATTCACTCGGACACCCGGCCCTATCCCTGTCAGTACTGTGGCAA

[0235] AAGATTCCACCAGAAGTCAGATATGAAGAAACACACCTTCATCCACACAGGTGAGAAGCCCCACAAAT

[0236] GCCAGGTGTGCGGCAAAGCCTTCAGTCAGAGCTCCAACCTCATCACTCATAGCAGAAAGCACACAG

[0237] GCTTCAAGCCCTTTGGCTGTGACCTGTGTGGGAAGGGCTTCCAGAGGAAGGTGGATCTCAGGAGGC

[0238] ACCGAGAGACTCAGCATGGACTCAAATGA

[0239] Gfi1 may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 10

[0240] SEQ ID NO: 10

[0241] ATGCCTAGGAGTTTCCTGGTGAAGAGCAAGAAGGCCCATTCTTACCACCAGCCCCGATCTCCTGGGC

[0242] CAGACTACAGCTTGAGACTGGAAACCGTGCCTGCCCCCGGTCGGGCCGAGGGAGGAGCAGTGAGC

[0243] GCAGGCGAGAGCAAAATGGAACCTAGGGAGAGACTGTCCCCCGACAGTCAGCTGACAGAGGCCCC

[0244] CGACAGAGCTAGCGCCAGCCCTAACTCATGTGAGGGGTCCGTGTGCGATCCCTGTAGCGAGTTTGA

[0245] GGACTTTTGGAGACCACCAAGCCCCAGCGTGAGCCCTGCCTCTGAGAAATCCCTGTGTAGATCTCTG

[0246] GACGAGGCTCAGCCCTACACCCTGCCATTCAAGCCCTACGCCTGGTCTGGCCTGGCCGGATCTGAT CTGCGGCATCTGGTGCAGAGTTACAGGCAGTGCTCCGCCCTGGAGAGATCAGCAGGCCTGAGCCTG TTCTGTGAGAGAGGGAGCGAGCCTGGACGGCCAGCCGCTAGATACGGCCCAGAACAGGCCGCAGG AGGAGCCGGCGCTGGGCAGCCTGGGAGCTGTGGTGTCGCCGGAGGAGCTACCAGCGCCGCAGGC

[0247] CTGGGCCTGTACGGGGACTTCGCACCCGCCGCCGCCGGGCTGTACGAGCGCCCCTCTACAGCCGC CGGCAGACTGTACCAGGATCACGGCCACGAACTGCATGCCGACAAGTCCGTGGGCGTGAAAGTGGA ATCTGAGCTGCTGTGCACACGGCTGCTGCTGGGCGGGGGAAGCTACAAGTGTATCAAGTGTAGTAA

[0248] GGTCTTCAGTACCCCTCATGGACTGGAGGTGCACGTGCGGAGGTCCCACAGCGGCACCAGGCCCTT CGCCTGTGAGATGTGCGGAAAGACCTTCGGGCATGCCGTGTCTCTTGAGCAGCACAAGGCTGTGCA CTCCCAGGAGAGAAGCTTCGACTGCAAAATCTGTGGGAAGTCCTTCAAGAGGTCTTCAACACTTTCT

[0249] ACCCACCTGCTGATCCACAGCGACACCAGGCCCTACCCTTGCCAGTACTGCGGTAAGAGATTTCACC AGAAATCCGACATGAAAAAGCATACATTTATCCACACCGGAGAGAAACCTCACAAATGTCAAGTGTGT GGGAAGGCTTTCTCCCAGAGCAGTAACCTGATCACTCACAGCAGGAAACACACTGGGTTCAAGCCTT

[0250] TCGGCTGCGACCTGTGCGGAAAGGGATTCCAGAGGAAAGTGGATCTGAGGAGACACCGCGAGACA CAGCACGGCCTCAAGTGA

[0251] Gfi1 may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 58

[0252] SEQ ID NO: 58

[0253] ATGCCTAGAAGCTTCCTGGTCAAGAGCAAGAAGGCCCACAGCTACCACCAGCCAAGAAGCCCTGGA CCTGACTACAGCCTGAGACTGGAAACCGTTCCTGCTCCTGGCAGAGCTGAAGGCGGAGCTGTTTCT GCTGGCGAGAGCAAGATGGAACCCAGAGAGAGACTGAGCCCCGACAGCCAGCTTACAGAGGCCCC

[0254] TGATAGAGCCAGCGCCTCTCCTAACTCTTGCGAGGGCTCTGTGTGCGACCCTTGCAGCGAGTTCGA GGACTTTTGGAGGCCACCTTCTCCTAGCGTGTCCCCAGCCTCTGAGAAGTCCCTGTGTAGAAGCCTG GATGAGGCCCAGCCTTACACACTGCCCTTCAAGCCTTACGCTTGGAGCGGCCTGGCTGGCTCTGAT

[0255] CTGAGACATCTGGTGCAGAGCTACAGACAGTGCAGCGCCCTGGAAAGATCTGCCGGCCTGTCTCTG TTTTGCGAGAGAGGATCTGAGCCTGGCAGACCTGCTGCTAGATACGGACCTGAACAAGCTGCCGGC GGTGCTGGTGCTGGACAACCTGGATCTTGTGGTGTTGCTGGCGGCGCTACATCTGCTGCTGGACTG

[0256] GGACTGTACGGCGATTTCGCTCCTGCTGCAGCTGGCCTGTACGAGAGGCCTTCTACAGCTGCTGGC AGACTGTACCAGGATCACGGACACGAGCTGCACGCCGATAAGTCTGTGGGCGTGAAGGTGGAAAGC GAGCTGCTGTGTACCAGACTGCTGCTCGGCGGAGGCAGCTACAAGTGCATCAAGTGCAGCAAGGTG

[0257] TTCAGCACCCCTCACGGCCTGGAAGTGCATGTGCGGAGATCTCACAGCGGCACCAGACCTTTCGCC TGCGAGATGTGTGGCAAGACATTCGGCCACGCCGTGTCTCTGGAACAGCACAAGGCTGTGCACTCC CAAGAGAGAAGCTTCGACTGCAAGATCTGCGGCAAGAGCTTCAAGAGAAGCAGCACCCTGAGCACC

[0258] CATCTGCTGATCCACTCCGACACCAGGCCTTATCCTTGCCAGTACTGTGGCAAGCGGTTCCACCAGA AAAGCGACATGAAGAAGCACACCTTCATCCACACCGGCGAGAAGCCCCACAAGTGTCAAGTGTGCG GCAAGGCCTTCAGCCAGAGCAGCAACCTGATCACACACAGCAGAAAGCACACCGGCTTCAAGCCCT

[0259] TCGGCTGTGACCTGTGTGGAAAGGGCTTCCAGAGAAAGGTGGACCTGAGAAGGCACAGAGAGACA CAGCACGGCCTGAAG

[0260] The functional variant of Gfi 1 may comprise an amino acid sequence at least 70% identical to SEQ ID NO: 6 or SEQ ID NO: 7. The functional variant of Gfi1 may comprise an amino acid sequence at least 80% identical to SEQ ID NO: 6 or SEQ ID NO: 7. The functional variant of Gfi1 may comprise an amino acid sequence at least 85% identical to SEQ ID NO: 6 or SEQ ID NO: 7. The functional variant of Gfi1 may comprise an amino acid sequence at least 90% identical to SEQ ID NO: 6 or SEQ ID NO: 7. The functional variant of Gfi1 may comprise an amino acid sequence at least 95% identical to SEQ ID NO: 6 or SEQ ID NO: 7. The functional variant of Gfi1 may comprise an amino acid sequence at least 96% identical to SEQ ID NO: 6 or SEQ ID NO: 7. The functional variant of Gfi1 may comprise an amino acid sequence at least 97% identical to SEQ ID NO: 6 or SEQ ID NO: 7. The functional variant of Gfi1 may comprise an amino acid sequence at least 98% identical to SEQ ID NO: 6 or SEQ ID NO: 7. The functional variant of Gfi1 may comprise an amino acid sequence at least 99% identical to SEQ ID NO: 6 or SEQ ID NO: 7. SEQ ID NO: 6 and SEQ ID NO: 7 share 370 identical amino acids out of 423 and thus are at least 87% identical to one another. The nucleic acid sequence may comprise any nucleic acid sequence encoding a functional variant of Gfi1 . Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 70% identical to SEQ ID NO: 6 or SEQ ID NO: 7. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 87% identical to SEQ ID NO: 6 or SEQ ID NO: 7. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 95% identical to SEQ ID NO: 6 or SEQ ID NO: 7.

[0261] The functional variant of Gfi1 may consist essentially of an amino acid sequence at least 70% identical to SEQ ID NO: 6 or SEQ ID NO: 7. The functional variant of Gfi1 may consist essentially of any amino acid sequence described elsewhere herein as a sequence that the functional variant of Gfi 1 may comprise.

[0262] The nucleic acid sequence may comprise any nucleic acid sequence encoding Gfi 1 . Gfi1 may comprise an amino acid sequence according to SEQ ID NO: 6 or SEQ ID NO: 7. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 6 or SEQ ID NO: 7. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 6. Alternatively, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 7.

[0263] The nucleotide sequence encoding Gfi1 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0264] (a) SEQ ID NO: 6,

[0265] (b) SEQ ID NO: 7,

[0266] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 6 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 6, or

[0267] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 7 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 7.

[0268] The nucleotide sequence encoding Gfi 1 or a functional variant thereof may consist essentially of a nucleic acid sequence encoding:

[0269] (a) SEQ ID NO: 6,

[0270] (b) SEQ ID NO: 7,

[0271] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 6 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 6, or (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 7 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 7.

[0272] The nucleotide sequence encoding Gfi 1 ora functional variant thereof may consist essentially of any nucleic acid sequence described elsewhere herein as a sequence that may encode Gfi1 or functional variant of Gfi1.

[0273] The nucleotide sequence encoding Gfi1 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0274] (a) SEQ ID NO: 6,

[0275] (b) SEQ ID NO: 7,

[0276] (c) an amino acid sequence having at least 87% identify to SEQ ID NO: 6 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 6, or

[0277] (d) an amino acid sequence having at least 87% identify to SEQ ID NO: 7 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 7.

[0278] The nucleotide sequence encoding Gfi1 or a functional variant thereof may comprise:

[0279] (a) SEQ ID NO: 8,

[0280] (b) SEQ ID NO: 9,

[0281] (c) SEQ ID NO: 10,

[0282] (d) SEQ ID NO: 58 or

[0283] (d) a nucleotide sequence having at least 60% identity to SEQ ID NO: 8, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 6, or

[0284] (e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 9, SEQ ID NO: 10 or SEQ ID NO: 58, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 7.

[0285] The nucleotide sequence encoding Gfi1 or a functional variant thereof may comprise a nucleic acid sequence having at least 60% identity to SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10 or SEQ ID NO: 58. The nucleotide sequence having at least 60% identity to SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10 or SEQ ID NO: 58 may have at least 70%, 75%, 80%, 85%, 90% or 95% identity to SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10 or SEQ ID NO: 58, respectively. SEQ ID NO: 8 and SEQ ID NO: 9 share 1085 identical nucleotides out of 1276 and thus are at least 85% identical to one another. SEQ ID NO: 9 and SEQ ID NO: 10 share 981 identical nucleotides out of 1272 and therefore have at least 77% sequence identity to each other and encode the same protein sequence. SEQ ID NO: 9 and SEQ ID NO: 58 share 989 identical nucleotides out of 1272 and therefore have at least 77% sequence identity to each other and encode the same protein sequence. The non-identical nucleotides may represent silent mutations (i.e. mutations which do not alter the sequence of the encoded amino acid). The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid, for example by one or more conservative amino acid mutation. The non-identical nucleotides may alterthe amino acid sequence of the encoded amino acid by up to 20, up to 15, up to 10, up to 9, up to 8, up to 7, up to 6, up to 5, up to 4, up to 3, up to 2 or up to 1 conservative amino acid mutation. The nucleotide sequence encoding Gfi1 or a functional variant thereof may comprise:

[0286] (a) SEQ ID NO: 8,

[0287] (b) SEQ ID NO: 9,

[0288] (c) SEQ ID NO: 10,

[0289] (d) SEQ ID NO: 58 or

[0290] (d) a nucleotide sequence having at least 77% identity to SEQ ID NO: 8, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 6, or

[0291] (e) a nucleotide sequence having at least 77% identity to SEQ ID NO: 9, SEQ ID NO: 10 or SEQ ID NO: 58, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 7.

[0292] The nucleotide sequence encoding Gfi1 or a functional variant thereof may comprise:

[0293] (a) SEQ ID NO: 8,

[0294] (b) SEQ ID NO: 9,

[0295] (c) SEQ ID NO: 10

[0296] (d) SEQ ID NO: 58, or

[0297] (d) a nucleotide sequence having at least 85% identity to SEQ ID NO: 8, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 6, or

[0298] (e) a nucleotide sequence having at least 85% identity to SEQ ID NO: 9, SEQ ID NO: 10 or SEQ ID NO: 58, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 7.

[0299] The nucleic acid sequence may encode GfH .The nucleotide sequence encoding Gfi1 may comprise:

[0300] (a) SEQ ID NO: 8,

[0301] (b) SEQ ID NO: 9,

[0302] (c) SEQ ID NO: 10, or

[0303] (d) SEQ ID NO: 58.

[0304] The nucleic acid molecule may encode at least two transcription factors, or functional variants thereof, wherein one transcription factor is Gfi1 and wherein the at least two transcription factors further comprise at least one transcription factor selected from the group consisting of Pou4f3, Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

[0305] According to any aspect of the invention, the transcription factors may comprise:

[0306] (a) Gfi1 and Pou4f3;

[0307] (b) Gfi1 and Lhx3

[0308] (c) Gfi1 and Isl1 ;

[0309] (d) Gfi1 and Six2

[0310] (e) Gfi1 and Pknox2; or

[0311] (f) Gfi1 and Kcnip3. According to any aspect of the invention, the transcription factors may comprise:

[0312] (a) Gfi1 , Pou4f3 and Lhx3

[0313] (b) Gfi1 , Pou4f3 and Isl1 ;

[0314] (c) Gfi 1 , Pou4f3 and Six2

[0315] (d) Gfi1 , Pou4f3 and Pknox2; or

[0316] (e) Gfi1 , Pou4f3 and Kcnip3.

[0317] As used herein, “Lhx3” refers to LIM / homeobox protein Lhx3. In humans it is encoded by the LHX3 gene, also known as LIM3; CPHD3 and M2-LHX3. The mouse ortholog Lhx3 is also known as Lim3; P-LIM; mLIM3 and mLim-3. In humans, the Ensembl gene ID is ENSG00000107187. An example of a transcript is the Ensembl transcript ID ENST00000371746.9 and the UniProt ID is Q9UBR4-2; codon-optimised and alternatively spliced transcript variants are encompassed. In mice, the Ensembl gene ID is ENSMUSG00000026934. An example of a transcript is the Ensembl transcript ID ENSMUST00000028302.8 and the UniProt ID is P50481-2; codon-optimised and alternatively spliced transcript variants are encompassed. A previous study (Menendez et al. (2020)) reported that Lhx3 had no effect alone. Menendez et al. (2020) also reported that Lhx3 failed to enhance the effect of any of Atohl (i.e. Atohl alone), Atohl and Pou4f3, or Atohl , Pou4f3 and Gfi1 (i.e. GPA), when added as an additional transcription factor to these Atohl based approaches to cochlea hair cell reprogramming.

[0318] Lhx3 may refer to the human sequence having the following amino acid sequence, identified as SEQ ID NO: 11

[0319] SEQ ID NO: 11

[0320] MEARGELGPARESAGGDLLLALLARRADLRREIPLCAGCDQHILDRFILKALDRHWHSKCLKCSDCHTPL AERCFSRGESVYCKDDFFKRFGTKCAACQLGIPPTQWRRAQDFVYHLHCFACWCKRQLATGDEFYLM EDSRLVCKADYETAKQREAEATAKRPRTTITAKQLETLKSAYNTSPKPARHVREQLSSETGLDMRVVQVW FQNRRAKEKRLKKDAGRQRWGQYFRNMKRSRGGSKSDKDSVQEGQDSDAEVSFPDEPSLAEMGPAN GLYGSLGEPTQALGRPSGALGNFSLEHGGLAGPEQYRELRPGSPYGVPPSPAAPQSLPGPQPLLSSLVY PDTSLGLVPSGAPGGPPPMRVLAGNGPSSDLSTGSSGGYPDFPASPASWLDEVDHAQF

[0321] Lhx3 may refer to the mouse sequence having the following amino acid sequence, identified as SEQ ID NO: 12

[0322] SEQ ID NO: 12

[0323] MEARGELDPSRESAGGDLLLALLARRADLRREIPMCAGCDQHILDRFILKALDRHWHSKCLKCSDCHVPL AERCFSRGESVYCKDDFFKRFGTKCAACQLGIPPTQWRRAQDFVYHLHCFACWCKRQLATGDEFYLM EDSRLVCKADYETAKQREAEATAKRPRTTITAKQLETLKSAYNTSPKPARHVREQLSSETGLDMRVVQVW FQNRRAKEKRLKKDAGRQRWGQYFRNMKRSRGSSKSDKDSIQEGQDSDAEVSFTDEPSMADMGPAN GLYSSLGEPAPALGRPVGGLGSFTLDHGGLTGPEQYRELRPGSPYGIPPSPAAPQSLPGPQPLLSSLVYP DTNLSLVPSGPPGGPPPMRVLAGNGPSSDLSTESSSGYPDFPASPASWLDEVDHAQF

[0324] Lhx3 may be encoded by the following human coding sequence, identified as SEQ ID NO: 13 SEQ ID NO: 13

[0325] ATGGAGGCGCGCGGGGAGCTGGGCCCGGCCCGGGAGTCGGCGGGAGGCGACCTGCTGCTAGCAC

[0326] TGCTGGCGCGGAGGGCGGACCTGCGCCGAGAGATCCCGCTGTGCGCTGGCTGTGACCAGCACATC

[0327] CTGGACCGCTTCATCCTCAAGGCTCTGGACCGCCACTGGCACAGCAAGTGTCTCAAGTGCAGCGAC

[0328] TGCCACACGCCACTGGCCGAGCGCTGCTTCAGCCGAGGGGAGAGCGTTTACTGCAAGGACGACTTT

[0329] TTCAAGCGCTTCGGGACCAAGTGCGCCGCGTGCCAGCTGGGCATCCCGCCCACGCAGGTGGTGCG

[0330] CCGCGCCCAGGACTTCGTGTACCACCTGCACTGCTTTGCCTGCGTCGTGTGCAAGCGGCAGCTGGC

[0331] CACGGGCGACGAGTTCTACCTCATGGAGGACAGCCGGCTCGTGTGCAAGGCGGACTACGAAACCG

[0332] CCAAGCAGCGAGAGGCCGAGGCCACGGCCAAGCGGCCGCGCACGACCATCACCGCCAAGCAGCT

[0333] GGAGACGCTGAAGAGCGCTTACAACACCTCGCCCAAGCCGGCGCGCCACGTGCGCGAGCAGCTCT

[0334] CGTCCGAGACGGGCCTGGACATGCGCGTGGTGCAGGTTTGGTTCCAGAACCGCCGGGCCAAGGAG

[0335] AAGAGGCTGAAGAAGGACGCCGGCCGGCAGCGCTGGGGGCAGTATTTCCGCAACATGAAGCGCTC

[0336] CCGCGGCGGCTCCAAGTCGGACAAGGACAGCGTTCAGGAGGGGCAGGACAGCGACGCTGAGGTC

[0337] TCCTTCCCCGATGAGCCTTCCTTGGCGGAAATGGGCCCGGCCAATGGCCTCTACGGGAGCTTGGGG

[0338] GAACCCACCCAGGCCTTGGGCCGGCCCTCGGGAGCCCTGGGCAACTTCTCCCTGGAGCATGGAGG

[0339] CCTGGCAGGCCCAGAGCAGTACCGAGAGCTGCGTCCCGGCAGCCCCTACGGTGTCCCCCCATCCC

[0340] CCGCCGCCCCGCAGAGCCTCCCTGGCCCCCAGCCCCTCCTCTCCAGCCTGGTGTACCCAGACACC

[0341] AGCTTGGGCCTTGTGCCCTCGGGAGCCCCCGGCGGGCCCCCACCCATGAGGGTGCTGGCAGGGA

[0342] ACGGACCCAGTTCTGACCTATCCACGGGGAGCAGCGGGGGTTACCCCGACTTCCCTGCCAGCCCC

[0343] GCCTCCTGGCTGGATGAGGTAGACCACGCTCAGTTCTGA

[0344] Lhx3 may be encoded by the following mouse coding sequence, identified as SEQ ID NO: 14

[0345] SEQ ID NO: 14

[0346] ATGGAAGCTCGCGGGGAGCTGGACCCGTCCCGGGAATCCGCGGGCGGAGACCTGCTGCTGGCGTT

[0347] GTTGGCGCGAAGGGCTGACCTGCGCCGAGAGATCCCGATGTGTGCAGGCTGTGACCAGCACATCTT

[0348] GGACCGTTTCATCCTTAAGGCTCTGGACCGACATTGGCACAGCAAGTGTCTCAAGTGCAGTGACTGC

[0349] CACGTCCCTCTGGCTGAGCGCTGCTTCAGCCGCGGGGAGAGCGTCTACTGCAAAGACGACTTCTTT

[0350] AAGCGCTTCGGGACCAAGTGCGCCGCATGCCAGCTGGGCATCCCGCCCACGCAGGTGGTGCGCCG

[0351] CGCCCAGGACTTCGTGTACCACCTGCATTGCTTCGCCTGCGTGGTCTGCAAGCGGCAGCTGGCCAC

[0352] GGGCGACGAGTTCTACCTCATGGAAGACAGCCGGCTGGTGTGCAAGGCGGACTACGAAACAGCCAA

[0353] GCAGCGAGAAGCCGAGGCCACAGCCAAGCGGCCGCGCACCACCATCACCGCCAAGCAGCTGGAGA

[0354] CGCTGAAGAGCGCCTACAACACTTCGCCCAAGCCGGCGCGCCACGTGCGCGAGCAGCTCTCCTCC

[0355] GAGACCGGCCTGGACATGCGAGTGGTGCAGGTGTGGTTCCAGAATCGCCGGGCTAAGGAAAAGAG

[0356] ACTGAAGAAAGACGCTGGCCGGCAGCGCTGGGGACAGTATTTCCGCAATATGAAGCGCTCCCGCGG

[0357] CAGTTCCAAGTCCGACAAGGACAGCATCCAGGAGGGACAAGACAGCGACGCCGAAGTCTCCTTCAC

[0358] TGATGAGCCGTCCATGGCTGACATGGGGCCTGCTAATGGCCTGTACAGCAGCCTGGGAGAGCCTGC

[0359] CCCTGCGTTGGGCCGGCCCGTAGGAGGCCTGGGCAGCTTTACCCTGGATCACGGAGGCTTGACGG

[0360] GTCCAGAGCAGTACCGAGAGCTACGCCCAGGCAGCCCCTATGGCATCCCCCCATCTCCTGCAGCCC

[0361] CCCAGAGCCTTCCTGGCCCCCAGCCTCTCCTCTCCAGCCTGGTATACCCAGACACCAACTTGAGCCT

[0362] TGTCCCTTCAGGGCCCCCAGGTGGACCCCCACCCATGAGGGTGCTGGCTGGAAATGGGCCCAGCT CCGACCTGTCCACAGAGAGCAGTTCTGGCTACCCAGACTTTCCTGCTAGCCCTGCTTCCTGGCTGGA

[0363] TGAAGTAGACCATGCTCAGTTCTGA

[0364] Lhx3 may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 15

[0365] SEQ ID NO: 15

[0366] ATGGAGGCTAGAGGCGAGCTGGACCCCAGCAGGGAGAGCGCAGGCGGGGACCTGCTGCTGGCCC

[0367] TGTTGGCCAGAAGAGCCGATCTGCGGAGAGAGATTCCCATGTGTGCTGGCTGCGACCAGCATATCCT

[0368] GGACAGGTTCATTCTGAAGGCCCTGGATAGACATTGGCATAGCAAGTGCCTGAAGTGTAGTGACTGC

[0369] CACGTGCCACTGGCCGAGAGGTGTTTTAGCAGGGGGGAGAGCGTGTACTGTAAGGATGATTTCTTTA

[0370] AGAGATTCGGAACTAAGTGTGCCGCCTGTCAGCTGGGAATTCCACCCACTCAGGTGGTGCGGAGAG

[0371] CCCAGGATTTTGTATACCACCTGCACTGCTTTGCCTGCGTGGTGTGCAAGAGACAGCTGGCCACTGG

[0372] CGACGAGTTCTACCTGATGGAGGACTCTCGGCTGGTGTGTAAGGCAGACTACGAGACAGCCAAGCA

[0373] GCGGGAGGCTGAAGCCACTGCCAAGAGGCCACGAACCACCATCACCGCCAAACAGCTGGAGACAC

[0374] TGAAGTCCGCCTATAACACATCTCCCAAACCTGCAAGGCACGTGAGAGAGCAGCTGAGCAGCGAAAC

[0375] CGGACTGGACATGAGGGTTGTGCAGGTGTGGTTCCAGAACAGAAGAGCCAAGGAGAAAAGACTGAA

[0376] GAAGGACGCAGGCAGACAGAGATGGGGGCAGTACTTCAGGAATATGAAGAGAAGTAGGGGGAGCAG

[0377] CAAGAGCGATAAAGACTCTATCCAGGAGGGCCAGGACTCTGACGCAGAGGTGAGCTTCACTGATGA

[0378] GCCATCTATGGCCGACATGGGACCCGCCAACGGCCTGTACAGCTCTCTGGGCGAACCAGCACCCGC

[0379] CCTGGGCCGGCCTGTTGGCGGGCTTGGCTCTTTCACCCTGGACCATGGCGGCCTGACCGGCCCAG

[0380] AGCAGTATAGGGAGTTGCGACCCGGGAGCCCCTATGGCATCCCTCCCAGTCCCGCTGCTCCTCAGT

[0381] CCCTGCCCGGCCCCCAGCCTCTGCTCAGTTCCCTGGTGTACCCTGATACCAACCTGTCCCTGGTCC

[0382] CTTCCGGACCACCCGGAGGTCCCCCTCCCATGCGCGTGCTGGCCGGCAACGGCCCTAGCAGTGAC

[0383] CTGTCTACTGAGAGCTCCAGCGGATATCCCGACTTCCCAGCCAGCCCTGCCAGCTGGCTAGACGAA

[0384] GTGGACCACGCCCAGTTCTGA

[0385] Lhx3 may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 59

[0386] SEQ ID NO: 59

[0387] ATGGAAGCTAGAGGCGAGCTGGACCCTAGCAGAGAATCTGCTGGCGGAGATCTGCTGCTGGCTCTG

[0388] CTTGCTAGAAGGGCTGACCTGAGAAGAGAAATCCCCATGTGCGCCGGCTGCGACCAGCACATCCTG

[0389] GACAGATTCATCCTGAAGGCCCTGGACAGGCACTGGCACAGCAAGTGCCTGAAGTGCAGCGACTGT

[0390] CACGTGCCACTGGCCGAGAGATGTTTCAGCAGAGGCGAGAGCGTGTACTGCAAGGACGACTTCTTC

[0391] AAGAGATTCGGCACCAAGTGCGCCGCCTGCCAGCTTGGAATTCCTCCTACACAGGTTGTGCGGAGA

[0392] GCCCAGGACTTCGTGTACCATCTGCACTGCTTCGCCTGCGTCGTGTGCAAGAGACAGCTGGCTACA

[0393] GGCGACGAGTTCTACCTGATGGAAGATAGCAGACTTGTGTGCAAGGCCGACTACGAGACAGCCAAG

[0394] CAGAGAGAGGCTGAGGCCACAGCCAAGAGGCCTAGAACCACAATCACCGCCAAGCAGCTGGAAAC

[0395] CCTGAAGTCCGCCTACAACACAAGCCCCAAGCCTGCTAGACACGTGCGCGAACAGCTGTCTAGCGA

[0396] GACAGGCCTGGACATGAGAGTGGTGCAAGTGTGGTTCCAGAACAGAAGGGCCAAAGAGAAGCGGC

[0397] TGAAGAAGGACGCCGGCAGACAGAGATGGGGCCAGTACTTCAGAAACATGAAGAGAAGCAGGGGC

[0398] AGCAGCAAGAGCGACAAGGACAGCATCCAAGAAGGCCAGGACAGCGACGCTGAGGTGTCCTTCAC

[0399] AGACGAGCCTAGCATGGCCGATATGGGCCCTGCTAACGGCCTGTACTCTAGCCTGGGAGAACCTGCT CCTGCTCTGGGCAGACCTGTTGGAGGCCTGGGATCTTTCACACTGGATCACGGCGGACTGACAGGC CCCGAGCAGTATAGAGAACTGAGGCCTGGCAGCCCCTACGGCATTCCTCCAAGTCCTGCTGCTCCTC AGTCTCTGCCTGGACCTCAACCTCTGCTGTCCAGCCTGGTGTACCCTGACACCAACCTGAGCCTGGT GCCTTCTGGACCTCCTGGTGGACCTCCACCTATGAGAGTGCTGGCTGGCAACGGACCTAGCAGCGA CCTGTCTACAGAGAGCAGCAGCGGCTACCCTGACTTCCCAGCTTCTCCTGCTAGCTGGCTGGACGA AGTGGATCACGCTCAGTTC

[0400] The functional variant of Lhx3 may comprise an amino acid sequence at least 70% identical to SEQ ID NO: 11 or SEQ ID NO: 12. The functional variant of Lhx3 may comprise an amino acid sequence at least 80% identical to SEQ ID NO: 11 or SEQ ID NO: 12. The functional variant of Lhx3 may comprise an amino acid sequence at least 85% identical to SEQ ID NO: 11 or SEQ ID NO: 12. The functional variant of Lhx3 may comprise an amino acid sequence at least 90% identical to SEQ ID NO: 11 or SEQ ID NO: 12. The functional variant of Lhx3 may comprise an amino acid sequence at least 95% identical to SEQ ID NO: 11 or SEQ ID NO: 12. The functional variant of Lhx3 may comprise an amino acid sequence at least 96% identical to SEQ ID NO: 11 or SEQ ID NO: 12. The functional variant of Lhx3 may comprise an amino acid sequence at least 97% identical to SEQ ID NO: 11 or SEQ ID NO: 12. The functional variant of Lhx3 may comprise an amino acid sequence at least 98% identical to SEQ ID NO: 11 or SEQ ID NO: 12. The functional variant of Lhx3 may comprise an amino acid sequence at least 99% identical to SEQ ID NO: 11 or SEQ ID NO: 12. SEQ ID NO: 11 and SEQ ID NO: 12 share 378 identical amino acids out of 402 and thus are at least 94% identical to one another. The nucleic acid sequence may comprise any nucleic acid sequence encoding a functional variant of Lhx3. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 70% identical to SEQ ID NO: 11 or SEQ ID NO: 12. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 94% identical to SEQ ID NO: 11 or SEQ ID NO: 12. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 95% identical to SEQ ID NO: 11 or SEQ ID NO: 12.

[0401] The functional variant of Lhx3 may consist essentially of an amino acid sequence at least 70% identical to SEQ ID NO: 11 or SEQ ID NO: 12. The functional variant of Lhx3 may consist essentially of any amino acid sequence described elsewhere herein as a sequence that the functional variant of Lhx3 may comprise.

[0402] The nucleic acid sequence may comprise any nucleic acid sequence encoding Lhx3. Lhx3 may comprise an amino acid sequence according to SEQ ID NO: 11 or SEQ ID NO: 12. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 11 or SEQ ID NO: 12. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 11 . Alternatively, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 12.

[0403] The nucleotide sequence encoding Lhx3 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0404] (a) SEQ ID NO: 11 ,

[0405] (b) SEQ ID NO: 12, (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 11 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 11 , or

[0406] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 12 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 12.

[0407] The nucleotide sequence encoding Lhx3 or a functional variant thereof may consist essentially of a nucleic acid sequence encoding:

[0408] (a) SEQ ID NO: 11 ,

[0409] (b) SEQ ID NO: 12,

[0410] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 11 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 11 , or

[0411] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 12 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 12.

[0412] The nucleotide sequence encoding Lhx3 or a functional variant thereof may consist essentially of any nucleic acid sequence described elsewhere herein as a sequence that may encode Lhx3 or functional variant of Lhx3.

[0413] The nucleotide sequence encoding Lhx3 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0414] (a) SEQ ID NO: 11 ,

[0415] (b) SEQ ID NO: 12,

[0416] (c) an amino acid sequence having at least 94% identify to SEQ ID NO: 11 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 11 , or

[0417] (d) an amino acid sequence having at least 94% identify to SEQ ID NO: 12 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 12.

[0418] The nucleotide sequence encoding Lhx3 or a functional variant thereof may comprise:

[0419] (a) SEQ ID NO: 13,

[0420] (b) SEQ ID NO: 14,

[0421] (c) SEQ ID NO: 15,

[0422] (d) SEQ ID NO: 59 or

[0423] (d) a nucleotide sequence having at least 60% identity to SEQ ID NO: 13, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 11 , or

[0424] (e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 14, SEQ ID NO: 15 or SEQ ID NO: 59, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 12.

[0425] The nucleotide sequence encoding Lhx3 or a functional variant thereof may comprise a nucleic acid sequence having at least 60% identity to SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15 or SEQ ID NO: 59. The nucleotide sequence having at least 60% identity to SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15 or SEQ ID NO: 59 may have at least 70%, 75%, 80%, 85%, 90% or 95% identity to SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15 or SEQ ID NO: 59, respectively. SEQ ID NO: 13 and SEQ ID NO: 14 share 1067 identical nucleotides out of 1209 and thus are at least 88% identical to one another. SEQ ID NO: 14 and SEQ ID NO: 15 share 943 identical nucleotides out of 1209 and therefore have at least 77% sequence identity to each other and encode the same protein sequence. SEQ ID NO: 14 and SEQ ID NO: 59 share 974 identical nucleotides out of 1209 and therefore have at least 80% sequence identity to each other and encode the same protein sequence. The non-identical nucleotides may represent silent mutations (i.e. mutations which do not alter the sequence of the encoded amino acid). The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid, for example by one or more conservative amino acid mutation. The non-identical nucleotides may alterthe amino acid sequence of the encoded amino acid by up to 20, up to 15, up to 10, up to 9, up to 8, up to 7, up to 6, up to 5, up to 4, up to 3, up to 2 or up to 1 conservative amino acid mutation.

[0426] The nucleotide sequence encoding Lhx3 or a functional variant thereof may comprise:

[0427] (a) SEQ ID NO: 13,

[0428] (b) SEQ ID NO: 14,

[0429] (c) SEQ ID NO: 15,

[0430] (d) SEQ ID NO: 59, or

[0431] (d) a nucleotide sequence having at least 77% identity to SEQ ID NO: 13, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 11 , or

[0432] (e) a nucleotide sequence having at least 80% identity to SEQ ID NO: 14, SEQ ID NO: 15 OR SEQ ID NO: 59, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 12.

[0433] The nucleotide sequence encoding Lhx3 or a functional variant thereof may comprise:

[0434] (a) SEQ ID NO: 13,

[0435] (b) SEQ ID NO: 14,

[0436] (c) SEQ ID NO: 15,

[0437] (d) SEQ ID NO: 59, or

[0438] (d) a nucleotide sequence having at least 88% identity to SEQ ID NO: 13, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 11 , or

[0439] (e) a nucleotide sequence having at least 88% identity to SEQ ID NO: 14, SEQ ID NO: 15 or SEQ ID NO: 59, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 12.

[0440] The nucleic acid sequence may encode Lhx3.The nucleotide sequence encoding Lhx3 may comprise:

[0441] (a) SEQ ID NO: 13,

[0442] (b) SEQ ID NO: 14,

[0443] (c) SEQ ID NO: 15, or

[0444] (d) SEQ ID NO: 59.

[0445] The nucleic acid molecule may encode at least two transcription factors, or functional variants thereof, wherein one transcription factor is Lhx3 and wherein the at least two transcription factors further comprise at least one transcription factor selected from the group consisting of Pou4f3, Gfi 1 , Isl 1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

[0446] According to any aspect of the invention, the transcription factors may comprise:

[0447] (a) Lhx3 and Pou4f3;

[0448] (b) Lhx3 and Gfi1 ;

[0449] (c) Lhx3 and lsl1 ;

[0450] (d) Lhx3 and Six2;

[0451] (e) Lhx3 and Pknox2; or

[0452] (f) Lhx3 and Kcnip3.

[0453] According to any aspect of the invention, the transcription factors may comprise:

[0454] (a) Lhx3, Gfi1 and Pou4f3;

[0455] (b) Lhx3, Six2 and Pou4f3;

[0456] (c) Lhx3, Six2 and Gfi1 ;

[0457] (d) Lhx3, Six2 and Isl1 ;

[0458] (e) Lhx3, Six2 and Pknox2; or

[0459] (f) Lhx3, Six2 and Kcnip3.

[0460] As used herein, “ Isl1 ” refers to ISL LIM Homeobox 1 . In humans it is encoded by the ISL1 gene, also known as lsl-1 and ISLET1 . The mouse ortholog Isl1 is also known as ISL1 transcription factor, LIM / homeodomain. In humans, the Ensembl gene ID is ENSG00000016082. An example of a transcript is the Ensembl transcript ID ENST00000230658.12 and the UniProt ID is P61371 ; codon-optimised and alternatively spliced transcript variants are encompassed. In mice, the Ensembl gene ID is ENSMUSG00000042258. An example of a transcript is the Ensembl transcript ID ENSMUST00000036060.13 and the UniProt ID is P61372; codon-optimised and alternatively spliced transcript variants are encompassed. A previous study (Yamashita et al. (2018); see also WO2018 / 148071) reported that Isl1 alone failed to promote any conversion of support cells to hair cells. However, Yamashita et al. (2020) and WO2018 / 148071 also reported a synergistic effect when Isl1 was added to Atohl and WO2018 / 148071 describes Isl1 as a “cotranscription factor” that “synergistically enhances Atohl -mediated SC-to-HC conversion” accordingly.

[0461] Isl1 may refer to the human sequence having the following amino acid sequence, identified as SEQ ID NO: 16

[0462] SEQ ID NO: 16

[0463] MGDMGDPPKKKRLISLCVGCGNQIHDQYILRVSPDLEWHAACLKCAECNQYLDESCTCFVRDGKTYCKR DYIRLYGIKCAKCSIGFSKNDFVMRARSKVYHIECFRCVACSRQLIPGDEFALREDGLFCRADHDWERAS LGAGDPLSPLHPARPLQMAAEPISARQPALRPHVHKQPEKTTRVRTVLNEKQLHTLRTCYAANPRPDALM KEQLVEMTGLSPRVIRVWFQNKRCKDKKRSIMMKQLQQQQPNDKTNIQGMTGTPMVAASPERHDGGLQ ANPVEVQSYQPPWKVLSDFALQSDIDQPAFQQLVNFSEGGPGSNSTGSEVASMSSQLPDTPNSMVASPI EA Isl1 may refer to the mouse sequence having the following amino acid sequence, identified as SEQ ID NO: 17

[0464] SEQ ID NO: 17

[0465] MGDMGDPPKKKRLISLCVGCGNQIHDQYILRVSPDLEWHAACLKCAECNQYLDESCTCFVRDGKTYCKR

[0466] DYIRLYGIKCAKCSIGFSKNDFVMRARSKVYHIECFRCVACSRQLIPGDEFALREDGLFCRADHDWERAS

[0467] LGAGDPLSPLHPARPLQMAAEPISARQPALRPHVHKQPEKTTRVRTVLNEKQLHTLRTCYAANPRPDALM

[0468] KEQLVEMTGLSPRVIRVWFQNKRCKDKKRSIMMKQLQQQQPNDKTNIQGMTGTPMVAASPERHDGGLQ

[0469] ANPVEVQSYQPPWKVLSDFALQSDIDQPAFQQLVNFSEGGPGSNSTGSEVASMSSQLPDTPNSMVASPI EA

[0470] Isl1 may be encoded by the following human coding sequence, identified as SEQ ID NO: 18

[0471] SEQ ID NO: 18

[0472] ATGGGAGACATGGGAGATCCACCAAAAAAAAAACGTCTGATTTCCCTATGTGTTGGTTGCGGCAATCA

[0473] GATTCACGATCAGTATATTCTGAGGGTTTCTCCGGATTTGGAATGGCATGCGGCATGTTTGAAATGTGC

[0474] GGAGTGTAATCAGTATTTGGACGAGAGCTGTACATGCTTTGTTAGGGATGGGAAAACCTACTGTAAAA

[0475] GAGATTATATCAGGTTGTACGGGATCAAATGCGCCAAGTGCAGCATCGGCTTCAGCAAGAACGACTTC

[0476] GTGATGCGTGCCCGCTCCAAGGTGTATCACATCGAGTGTTTCCGCTGTGTGGCCTGCAGCCGCCAG

[0477] CTCATCCCTGGGGACGAATTTGCGCTTCGGGAGGACGGTCTCTTCTGCCGAGCAGACCACGATGTG

[0478] GTGGAGAGGGCCAGTCTAGGCGCTGGCGACCCGCTCAGTCCCCTGCATCCAGCGCGGCCACTGCA

[0479] AATGGCAGCGGAGCCCATCTCCGCCAGGCAGCCAGCCCTGCGGCCCCACGTCCACAAGCAGCCGG

[0480] AGAAGACCACCCGCGTGCGGACTGTGCTGAACGAGAAGCAGCTGCACACCTTGCGGACCTGCTAC

[0481] GCCGCAAACCCGCGGCCAGATGCGCTCATGAAGGAGCAACTGGTAGAGATGACGGGCCTCAGTCCC

[0482] CGTGTGATCCGGGTCTGGTTTCAAAACAAGCGGTGCAAGGACAAGAAGCGAAGCATCATGATGAAGC

[0483] AACTCCAGCAGCAGCAGCCCAATGACAAAACTAATATCCAGGGGATGACAGGAACTCCCATGGTGGC

[0484] TGCCAGTCCAGAGAGACACGACGGTGGCTTACAGGCTAACCCAGTGGAAGTACAAAGTTACCAGCC

[0485] ACCTTGGAAAGTACTGAGCGACTTCGCCTTGCAGAGTGACATAGATCAGCCTGCTTTTCAGCAACTG

[0486] GTCAATTTTTCAGAAGGAGGACCGGGCTCTAATTCCACTGGCAGTGAAGTAGCATCAATGTCCTCTCA ACTTCCAGATACACCTAACAGCATGGTAGCCAGTCCTATTGAGGCATGA

[0487] Isl1 may be encoded by the following mouse coding sequence, identified as SEQ ID NO: 19

[0488] SEQ ID NO: 19

[0489] ATGGGAGACATGGGCGATCCACCAAAAAAAAAACGTCTGATTTCCCTGTGTGTTGGTTGCGGCAATC

[0490] AAATTCACGACCAGTATATTCTGAGGGTTTCTCCGGATTTGGAGTGGCATGCAGCATGTTTGAAATGT

[0491] GCGGAGTGTAATCAGTATTTGGACGAAAGCTGTACGTGCTTTGTTAGGGATGGGAAAACCTACTGTAA

[0492] AAGAGATTATATCAGGTTGTACGGGATCAAATGCGCCAAGTGCAGCATAGGCTTCAGCAAGAACGACT

[0493] TCGTGATGCGTGCCCGCTCTAAGGTGTACCACATCGAGTGTTTCCGCTGTGTAGCCTGCAGCCGACA

[0494] GCTCATCCCGGGAGACGAATTCGCCCTGCGGGAGGATGGGCTTTTCTGCCGTGCAGACCACGATGT

[0495] GGTGGAGAGAGCCAGCCTGGGAGCTGGAGACCCTCTCAGTCCCTTGCATCCAGCGCGGCCTCTGC

[0496] AAATGGCAGCCGAACCCATCTCGGCTAGGCAGCCAGCTCTGCGGCCGCACGTCCACAAGCAGCCG GAGAAGACCACCCGAGTGCGGACTGTGCTCAACGAGAAGCAGCTGCACACCTTGCGGACCTGCTAT GCCGCCAACCCTCGGCCAGATGCGCTCATGAAGGAGCAACTAGTGGAGATGACGGGCCTCAGTCCC AGAGTCATCCGAGTGTGGTTTCAAAACAAGCGGTGCAAGGACAAGAAACGCAGCATCATGATGAAGC AGCTCCAGCAGCAGCAACCCAACGACAAAACTAATATCCAGGGGATGACAGGAACTCCCATGGTGGC TGCTAGTCCGGAGAGACATGATGGTGGTTTACAGGCTAACCCAGTAGAGGTGCAAAGTTACCAGCCG CCCTGGAAAGTACTGAGTGACTTCGCCTTGCAAAGCGACATAGATCAGCCTGCTTTTCAGCAACTGG TCAATTTTTCAGAAGGAGGACCAGGCTCTAATTCTACTGGCAGTGAAGTAGCATCGATGTCCTCGCAG CTCCCAGATACACCCAACAGCATGGTAGCCAGTCCTATTGAGGCATGA

[0497] Isl1 may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 20

[0498] SEQ ID NO: 20

[0499] ATGGAGGCTAGAGGCGAGCTGGACCCCAGCAGGGAGAGCGCAGGCGGGGACCTGCTGCTGGCCC TGTTGGCCAGAAGAGCCGATCTGCGGAGAGAGATTCCCATGTGTGCTGGCTGCGACCAGCATATCCT GGACAGGTTCATTCTGAAGGCCCTGGATAGACATTGGCATAGCAAGTGCCTGAAGTGTAGTGACTGC CACGTGCCACTGGCCGAGAGGTGTTTTAGCAGGGGGGAGAGCGTGTACTGTAAGGATGATTTCTTTA AGAGATTCGGAACTAAGTGTGCCGCCTGTCAGCTGGGAATTCCACCCACTCAGGTGGTGCGGAGAG CCCAGGATTTTGTATACCACCTGCACTGCTTTGCCTGCGTGGTGTGCAAGAGACAGCTGGCCACTGG CGACGAGTTCTACCTGATGGAGGACTCTCGGCTGGTGTGTAAGGCAGACTACGAGACAGCCAAGCA GCGGGAGGCTGAAGCCACTGCCAAGAGGCCACGAACCACCATCACCGCCAAACAGCTGGAGACAC TGAAGTCCGCCTATAACACATCTCCCAAACCTGCAAGGCACGTGAGAGAGCAGCTGAGCAGCGAAAC CGGACTGGACATGAGGGTTGTGCAGGTGTGGTTCCAGAACAGAAGAGCCAAGGAGAAAAGACTGAA GAAGGACGCAGGCAGACAGAGATGGGGGCAGTACTTCAGGAATATGAAGAGAAGTAGGGGGAGCAG CAAGAGCGATAAAGACTCTATCCAGGAGGGCCAGGACTCTGACGCAGAGGTGAGCTTCACTGATGA GCCATCTATGGCCGACATGGGACCCGCCAACGGCCTGTACAGCTCTCTGGGCGAACCAGCACCCGC CCTGGGCCGGCCTGTTGGCGGGCTTGGCTCTTTCACCCTGGACCATGGCGGCCTGACCGGCCCAG AGCAGTATAGGGAGTTGCGACCCGGGAGCCCCTATGGCATCCCTCCCAGTCCCGCTGCTCCTCAGT CCCTGCCCGGCCCCCAGCCTCTGCTCAGTTCCCTGGTGTACCCTGATACCAACCTGTCCCTGGTCC CTTCCGGACCACCCGGAGGTCCCCCTCCCATGCGCGTGCTGGCCGGCAACGGCCCTAGCAGTGAC CTGTCTACTGAGAGCTCCAGCGGATATCCCGACTTCCCAGCCAGCCCTGCCAGCTGGCTAGACGAA GTGGACCACGCCCAGTTCTGA

[0500] The functional variant of Isl1 may comprise an amino acid sequence at least 70% identical to SEQ ID NO: 16 or SEQ ID NO: 17. The functional variant of Isl1 may comprise an amino acid sequence at least 80% identical to SEQ ID NO: 16 or SEQ ID NO: 17. The functional variant of Isl1 may comprise an amino acid sequence at least 85% identical to SEQ ID NO: 16 or SEQ ID NO: 17. The functional variant of Isl1 may comprise an amino acid sequence at least 90% identical to SEQ ID NO: 16 or SEQ ID NO: 17. The functional variant of Isl1 may comprise an amino acid sequence at least 95% identical to SEQ ID NO: 16 or SEQ ID NO: 17. The functional variant of Isl1 may comprise an amino acid sequence at least 96% identical to SEQ ID NO: 16 or SEQ ID NO: 17. The functional variant of Isl1 may comprise an amino acid sequence at least 97% identical to SEQ ID NO: 16 or SEQ ID NO: 17. The functional variant of Isl1 may comprise an amino acid sequence at least 98% identical to SEQ ID NO: 16 or SEQ ID NO: 17. The functional variant of Isl1 may comprise an amino acid sequence at least 99% identical to SEQ ID NO: 16 or SEQ ID NO: 17. SEQ ID NO: 16 and SEQ ID NO: 17 share 349 identical amino acids out of 349 and thus are at least 99% identical to one another (specifically they are 100% identical to one another). The nucleic acid sequence may comprise any nucleic acid sequence encoding a functional variant Isl1 . Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 70% identical to SEQ ID NO: 16 or SEQ ID NO: 17. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 95% identical to SEQ ID NO: 16 or SEQ ID NO: 17. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 99% identical to SEQ ID NO: 16 or SEQ ID NO: 17.

[0501] The functional variant of Isl1 may consist essentially of an amino acid sequence at least 70% identical to SEQ ID NO: 16 or SEQ ID NO: 17. The functional variant of Isl 1 may consist essentially of any amino acid sequence described elsewhere herein as a sequence that the functional variant of Isl1 may comprise.

[0502] The nucleic acid sequence may comprise any nucleic acid sequence encoding Isl1 . Isl1 may comprise an amino acid sequence according to SEQ ID NO: 16 or SEQ ID NO: 17. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 16 or SEQ ID NO: 17. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 16. Alternatively, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 17.

[0503] The nucleotide sequence encoding Isl1 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0504] (a) SEQ ID NO: 16,

[0505] (b) SEQ ID NO: 17,

[0506] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 16 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 16, or

[0507] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 17 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 17.

[0508] The nucleotide sequence encoding Isl1 or a functional variant thereof may consist essentially of a nucleic acid sequence encoding:

[0509] (a) SEQ ID NO: 16,

[0510] (b) SEQ ID NO: 17,

[0511] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 16 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 16, or

[0512] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 17 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 17. The nucleotide sequence encoding Isl1 or a functional variant thereof may consist essentially of any nucleic acid sequence described elsewhere herein as a sequence that may encode Is 11 or functional variant of Isl 1 .

[0513] The nucleotide sequence encoding Isl1 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0514] (a) SEQ ID NO: 16,

[0515] (b) SEQ ID NO: 17,

[0516] (c) an amino acid sequence having at least 99% identify to SEQ ID NO: 16 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 16, or

[0517] (d) an amino acid sequence having at least 99% identify to SEQ ID NO: 17 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 17.

[0518] The nucleotide sequence encoding Isl1 or a functional variant thereof may comprise:

[0519] (a) SEQ ID NO: 18,

[0520] (b) SEQ ID NO: 19,

[0521] (c) SEQ ID NO: 20, or

[0522] (d) a nucleotide sequence having at least 60% identity to SEQ ID NO: 18, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 16, or

[0523] (e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 19 or SEQ ID NO: 20, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 17.

[0524] The nucleotide sequence encoding Isl1 or a functional variant thereof may comprise a nucleic acid sequence having at least 60% identity to SEQ ID NO: 18, SEQ ID NO: 19, or SEQ ID NO: 20. The nucleotide sequence having at least 60% identity to SEQ ID NO: 18, SEQ ID NO: 19, or SEQ ID NO: 20 may have at least 70%, 75%, 80%, 85%, 90% or 95% identity to SEQ ID NO: 18, SEQ ID NO: 19, or SEQ ID NO: 20, respectively. SEQ ID NO: 18 and SEQ ID NO: 19 share 977 identical nucleotides out of 1050 and thus are at least 93% identical to one another. SEQ ID NO: 19 and SEQ ID NO: 20 share 821 identical nucleotides out of 1050 and therefore have at least 78% sequence identity to each other and encode the same protein sequence. The non-identical nucleotides may represent silent mutations (i.e. mutations which do not alter the sequence ofthe encoded amino acid). The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid, for example by one or more conservative amino acid mutation. The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid by up to 20, up to 15, up to 10, up to 9, up to 8, up to 7, up to 6, upto 5, up to 4, up to 3, up to 2 or up to 1 conservative amino acid mutation.

[0525] The nucleotide sequence encoding Isl1 or a functional variant thereof may comprise:

[0526] (a) SEQ ID NO: 18,

[0527] (b) SEQ ID NO: 19,

[0528] (c) SEQ ID NO: 20, or

[0529] (d) a nucleotide sequence having at least 78% identity to SEQ ID NO: 18, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 16, or (e) a nucleotide sequence having at least 78% identity to SEQ ID NO: 19 or SEQ ID NO: 20, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 17.

[0530] The nucleotide sequence encoding Isl1 or a functional variant thereof may comprise:

[0531] (a) SEQ ID NO: 18,

[0532] (b) SEQ ID NO: 19,

[0533] (c) SEQ ID NO: 20, or

[0534] (d) a nucleotide sequence having at least 93% identity to SEQ ID NO: 18, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 16, or

[0535] (e) a nucleotide sequence having at least 93% identity to SEQ ID NO: 19 or SEQ ID NO: 20, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 17.

[0536] The nucleic acid sequence may encode Isl1 .

[0537] The nucleotide sequence encoding Isl1 may comprise:

[0538] (a) SEQ ID NO: 18,

[0539] (b) SEQ ID NO: 19, or

[0540] (c) SEQ ID NO: 20.

[0541] The nucleic acid molecule may encode at least two transcription factors, or functional variants thereof, wherein one transcription factor is Isl 1 and wherein the at least two transcription factors further comprise at least one transcription factor selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

[0542] According to any aspect of the invention, the transcription factors may comprise:

[0543] (a) Isl1 and Pou4f3;

[0544] (b) Isl1 and Gfi1 ;

[0545] (c) Isl1 and Six2;

[0546] (d) Isl1 and Lhx3;

[0547] (e) Isl1 and Pknox2; or

[0548] (f) Isl1 and Kcnip3.

[0549] According to any aspect of the invention, the transcription factors may comprise:

[0550] (a) Isl1 , Kcnip3 and Pou4f3;

[0551] (b) Isl1 , Kcnip3 and Gfi1 ;

[0552] (c) Isl1 , Kcnip3 and Six2;

[0553] (d) Isl1 , Kcnip3 and Lhx3; or

[0554] (e) Isl1 , Kcnip3 and Pknox2.

[0555] As used herein, “Six2” refers to SIX Homeobox 2. In humans it is encoded by the SIX2 gene, also known as Sine Oculis Homeobox Homolog 2; Homeobox Protein SIX2; Sine Oculis Homeobox (Drosophila) Homolog 2; and Sine Oculis Homeobox Homolog 2 (Drosophila). The mouse ortholog Six2 is also known as sine oculis-related homeobox 2. In humans, the Ensembl gene ID is ENSG00000170577. An example of a transcript is the Ensembl transcript ID ENST00000303077.7 and the UniProt ID is Q9NPC8; codon- optimised and alternatively spliced transcript variants are encompassed. In mice, the Ensembl gene ID is ENSMUSG00000024134. An example of a transcript is the Ensembl transcript ID ENSMUST00000163568.4 and the UniProt ID is Q62232; codon-optimised and alternatively spliced transcript variants are encompassed. Functional data concerning Six2 in cochlear hair cell reprogramming, either alone or in combination with Atohl , has not previously been reported. Previous commentators have included Six2 among lists of transcription factors they believe could have a role in increasing the maturity of immature hair cells produced using Atohl , without collecting any functional data to support this assertion. For example, Six2 is mentioned alongside 7 other transcription factors identified as candidates to promote maturation of Atohl induced hair cells by Shu & Zuo (2003) PLoS ONE 18(12): e0284685, but no functional data are disclosed. Further, Rai et al. (2022) lists Six2 alongside 6 other transcription factors said to be predicted as candidates to modulate alongside Atohl , but no functional data are disclosed. Additionally, WO2018 / 148071 describes Six2 as a “co-transcription factor” alleging that it “synergistically enhances Atohl -mediated SC-to-HC conversion” (in a list of around 50 other “co-transcription factors”) without disclosing any functional data to support this assertion.

[0556] Six2 may refer to the human sequence having the following amino acid sequence, identified as SEQ ID NO: 21

[0557] SEQ ID NO: 21 MSMLPTFGFTQEQVACVCEVLQQGGNIERLGRFLWSLPACEHLHKNESVLKAKAVVAFHRGNFRELYKIL ESHQFSPHNHAKLQQLWLKAHYIEAEKLRGRPLGAVGKYRVRRKFPLPRSIWDGEETSYCFKEKSRSVL REWYAHNPYPSPREKRELAEATGLTTTQVSNWFKNRRQRDRAAEAKERENNENSNSNSHNPLNGSGK SVLGSSEDEKTPSGTPDHSSSSPALLLSPPPPGLPSLHSLGHPPGPSAVPVPVPGGGGADPLQHHHGLQ DSILNPMSANLVDLGS

[0558] Six2 may refer to the mouse sequence having the following amino acid sequence, identified as SEQ ID NO: 22

[0559] SEQ ID NO: 22 MSMLPTFGFTQEQVACVCEVLQQGGNIERLGRFLWSLPACEHLHKNESVLKAKAVVAFHRGNFRELYKIL ESHQFSPHNHAKLQQLWLKAHYIEAEKLRGRPLGAVGKYRVRRKFPLPRSIWDGEETSYCFKEKSRSVL REWYAHNPYPSPREKRELAEATGLTTTQVSNWFKNRRQRDRAAEAKERENSENSNSSSHNPLASSLNG SGKSVLGSSEDEKTPSGTPDHSSSSPALLLSPPPPPGLPSLHSLGHPPGPSAVPVPVPGGGGADPLQHH HSLQDSILNPMSANLVDLGS

[0560] Six2 may be encoded by the following human coding sequence, identified as SEQ ID NO: 23

[0561] SEQ ID NO: 23 ATGTCCATGCTGCCCACCTTCGGCTTCACGCAGGAGCAAGTGGCGTGCGTGTGCGAGGTGCTGCAG

[0562] CAGGGCGGCAACATCGAGCGGCTGGGCCGCTTCCTGTGGTCGCTGCCCGCCTGCGAGCACCTTCA

[0563] CAAGAATGAAAGCGTGCTCAAGGCCAAGGCCGTGGTGGCCTTCCACCGCGGCAACTTCCGCGAGCT

[0564] CTACAAGATCCTGGAGAGCCACCAGTTCTCGCCGCACAACCACGCCAAGCTGCAGCAGCTGTGGCT

[0565] CAAGGCACACTACATCGAGGCGGAGAAGCTGCGCGGCCGACCCCTGGGCGCCGTGGGCAAATACC

[0566] GCGTGCGCCGCAAATTCCCGCTGCCGCGCTCCATCTGGGACGGCGAGGAGACCAGCTACTGCTTCA

[0567] AGGAAAAGAGTCGCAGCGTGCTGCGCGAGTGGTACGCGCACAACCCCTACCCTTCACCCCGCGAG

[0568] AAGCGTGAGCTGGCGGAGGCCACGGGCCTCACCACCACACAGGTCAGCAACTGGTTCAAGAACCG

[0569] GCGGCAGCGCGACCGGGCGGCCGAGGCCAAGGAAAGGGAGAACAACGAGAACTCCAATTCTAACA

[0570] GCCACAACCCGCTGAATGGCAGCGGCAAGTCGGTGTTAGGCAGCTCGGAGGATGAGAAGACTCCAT

[0571] CGGGGACGCCAGACCACTCATCATCCAGCCCCGCACTGCTCCTCAGCCCGCCGCCCCCTGGGCTG

[0572] CCGTCCCTGCACAGCCTGGGCCACCCTCCGGGCCCCAGCGCAGTGCCAGTGCCGGTGCCAGGCG

[0573] GAGGTGGAGCGGACCCACTGCAACACCACCATGGCCTGCAGGACTCCATCCTCAACCCCATGTCAG

[0574] CCAACCTCGTGGACCTGGGCTCCTAG

[0575] Six2 may be encoded by the following mouse coding sequence, identified as SEQ ID NO: 24

[0576] SEQ ID NO: 24

[0577] ATGTCCATGCTGCCCACCTTCGGCTTCACGCAGGAGCAAGTGGCGTGCGTGTGCGAGGTGCTGCAG

[0578] CAGGGCGGCAACATCGAGCGGCTGGGTCGCTTCCTGTGGTCGCTGCCCGCCTGCGAGCACCTCCA

[0579] CAAGAATGAAAGCGTGCTCAAGGCCAAGGCCGTGGTGGCCTTCCACCGGGGCAACTTCCGCGAGC

[0580] TCTACAAAATCCTGGAGAGCCACCAGTTCTCGCCGCACAACCACGCCAAGCTGCAGCAGTTGTGGC

[0581] TCAAGGCGCACTACATCGAGGCGGAGAAGCTGCGCGGCCGGCCGCTGGGCGCCGTGGGCAAGTAC

[0582] CGCGTGCGGCGCAAGTTCCCGCTGCCCCGCTCCATCTGGGACGGCGAGGAGACCAGCTACTGCTT

[0583] CAAGGAGAAGAGCCGCAGCGTGCTGCGCGAGTGGTACGCTCACAACCCCTACCCGTCGCCACGAG

[0584] AGAAGCGCGAGCTGGCCGAGGCCACCGGCCTCACCACCACGCAAGTCAGCAACTGGTTCAAGAAC

[0585] CGGCGGCAGCGCGACAGGGCGGCCGAGGCCAAGGAAAGGGAGAACAGCGAGAACTCCAATTCCA

[0586] GCAGCCACAACCCGCTGGCTTCCTCGCTCAATGGCAGTGGCAAGTCGGTGCTAGGCAGTTCCGAGG

[0587] ATGAGAAGACGCCGTCGGGGACTCCAGACCACTCGTCGTCCAGTCCCGCTCTGTTGCTCAGCCCGC

[0588] CGCCGCCCCCTGGGCTGCCTTCCCTGCACAGCCTGGGCCACCCTCCGGGCCCGAGCGCAGTACCC

[0589] GTACCAGTGCCCGGTGGAGGCGGCGCGGACCCACTGCAGCATCACCACAGCCTGCAGGACTCCAT

[0590] ACTCAACCCCATGTCGGCCAACCTTGTGGACCTGGGCTCCTAG

[0591] Six2 may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 25

[0592] SEQ ID NO: 25

[0593] ATGAGTATGCTGCCCACCTTTGGGTTCACCCAGGAGCAGGTGGCCTGTGTGTGTGAGGTGCTACAG

[0594] CAGGGGGGCAACATTGAGAGACTGGGCCGCTTCTTGTGGTCACTGCCAGCTTGCGAACACCTGCAC

[0595] AAGAACGAATCTGTGCTGAAGGCTAAGGCAGTGGTGGCTTTCCATAGAGGGAATTTCAGGGAACTGT

[0596] ACAAGATTCTGGAGAGTCACCAGTTCTCCCCTCACAATCACGCCAAGCTTCAGCAGCTCTGGCTGAA

[0597] GGCTCATTACATCGAGGCTGAGAAGCTGCGGGGACGCCCACTGGGAGCCGTGGGCAAGTACAGGG

[0598] TCAGGAGAAAGTTTCCCCTGCCTCGATCCATCTGGGACGGCGAGGAAACCTCTTATTGCTTTAAGGA GAAAAGCAGATCCGTGCTGAGAGAGTGGTACGCCCATAACCCATACCCCTCTCCTAGGGAGAAGAGA GAACTGGCCGAGGCCACCGGCCTGACTACCACACAGGTGTCCAACTGGTTCAAGAATAGGCGCCAG AGGGACCGGGCCGCTGAAGCCAAGGAGCGGGAGAACAGCGAGAACAGCAACTCCTCTTCACACAA TCCCCTCGCAAGTAGCCTGAACGGCTCAGGCAAGAGCGTGCTGGGCTCCTCTGAGGACGAAAAGAC CCCAAGCGGCACCCCCGATCACAGCAGCAGCAGCCCTGCTCTGCTCCTGAGCCCTCCTCCTCCCCC CGGACTGCCTAGCCTGCACAGCCTGGGACATCCACCTGGCCCCTCCGCCGTGCCCGTGCCCGTGC CCGGCGGCGGAGGCGCTGACCCCCTCCAACACCACCACAGCCTCCAGGATAGCATTCTGAACCCCA TGTCCGCTAATCTGGTGGACCTGGGCTCCTAG

[0599] Six2 may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 60

[0600] SEQ ID NO: 60

[0601] ATGAGCATGCTGCCCACCTTCGGCTTCACCCAAGAACAGGTGGCCTGTGTGTGCGAGGTTCTGCAG CAAGGCGGCAACATCGAGAGACTGGGCAGATTCCTTTGGAGCCTGCCAGCCTGCGAGCATCTGCAC AAGAACGAGTCTGTGCTGAAGGCCAAGGCCGTGGTGGCTTTCCACAGAGGCAACTTCAGAGAGCTG TACAAGATCCTGGAATCCCACCAGTTCAGCCCTCACAACCACGCCAAACTGCAGCAGCTGTGGCTGA AAGCCCACTACATCGAGGCCGAGAAGCTGAGAGGTAGACCTCTGGGAGCTGTGGGCAAGTACAGAG TGCGGAGAAAGTTCCCTCTGCCTAGATCCATCTGGGACGGCGAGGAAACCAGCTACTGCTTCAAAGA AAAGTCTCGGAGCGTGCTGAGAGAGTGGTACGCTCACAACCCCTATCCATCTCCAAGAGAGAAGAGA GAGCTGGCCGAGGCCACAGGCCTGACCACAACACAAGTGTCCAACTGGTTCAAGAACAGAAGGCA GAGAGACAGAGCCGCCGAGGCTAAAGAGAGAGAGAACTCCGAGAACAGCAACAGCAGCAGCCACA ATCCTCTGGCCTCTAGCCTGAACGGCAGCGGAAAATCTGTGCTGGGCAGCAGCGAGGACGAAAAGA CACCTAGCGGCACCCCTGACCACTCCTCTAGTTCTCCAGCTCTGCTGCTGAGCCCTCCTCCTCCACC TGGATTGCCTTCTCTGCACTCTCTGGGACACCCTCCAGGACCATCTGCTGTGCCTGTTCCAGTTCCT GGCGGAGGCGGAGCTGATCCTCTGCAGCATCATCACAGCCTGCAGGACAGCATCCTGAATCCTATGA GCGCCAACCTGGTGGACCTGGGCTCTTAA

[0602] The functional variant of Six2 may comprise an amino acid sequence at least 70% identical to SEQ ID NO: 21 or SEQ ID NO: 22. The functional variant of Six2 may comprise an amino acid sequence at least 80% identical to SEQ ID NO: 21 or SEQ ID NO: 22. The functional variant of Six2 may comprise an amino acid sequence at least 85% identical to SEQ ID NO: 21 or SEQ ID NO: 22. The functional variant of Six2 may comprise an amino acid sequence at least 90% identical to SEQ ID NO: 21 or SEQ ID NO: 22. The functional variant of Six2 may comprise an amino acid sequence at least 95% identical to SEQ ID NO: 21 or SEQ ID NO: 22. The functional variant of Six2 may comprise an amino acid sequence at least 96% identical to SEQ ID NO: 21 or SEQ ID NO: 22. The functional variant of Six2 may comprise an amino acid sequence at least 97% identical to SEQ ID NO: 21 or SEQ ID NO: 22. The functional variant of Six2 may comprise an amino acid sequence at least 98% identical to SEQ ID NO: 21 or SEQ ID NO: 22. The functional variant of Six2 may comprise an amino acid sequence at least 99% identical to SEQ ID NO: 21 or SEQ ID NO: 22. SEQ ID NO: 21 and SEQ ID NO: 22 share 288 identical amino acids out of 296 and thus are at least 97% identical to one another. The nucleic acid sequence may comprise any nucleic acid sequence encoding a functional variant Six2. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 70% identical to SEQ ID NO: 21 or SEQ ID NO: 22. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 95% identical to SEQ ID NO: 21 or SEQ ID NO: 22. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 97% identical to SEQ ID NO: 21 or SEQ ID NO: 22.

[0603] The functional variant of Six2 may consist essentially of an amino acid sequence at least 70% identical to SEQ ID NO: 21 or SEQ ID NO: 22. The functional variant of Six2 may consist essentially of any amino acid sequence described elsewhere herein as a sequence that the functional variant of Six2 may comprise.

[0604] The nucleic acid sequence may comprise any nucleic acid sequence encoding Six2. Six2 may comprise an amino acid sequence according to SEQ ID NO: 21 or SEQ ID NO: 22. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 21 or SEQ ID NO: 22. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 21 . Alternatively, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 22.

[0605] The nucleotide sequence encoding Six2 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0606] (a) SEQ ID NO: 21 ,

[0607] (b) SEQ ID NO: 22,

[0608] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 21 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 21 , or

[0609] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 22 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 22.

[0610] The nucleotide sequence encoding Six2 or a functional variant thereof may consist essentially of a nucleic acid sequence encoding:

[0611] (a) SEQ ID NO: 21 ,

[0612] (b) SEQ ID NO: 22,

[0613] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 21 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 21 , or

[0614] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 22 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 22.

[0615] The nucleotide sequence encoding Six2 or a functional variant thereof may consist essentially of any nucleic acid sequence described elsewhere herein as a sequence that may encode Six2 or functional variant of Six2.

[0616] The nucleotide sequence encoding Six2 or a functional variant thereof may comprise a nucleic acid sequence encoding: (a) SEQ ID NO: 21 ,

[0617] (b) SEQ ID NO: 22,

[0618] (c) an amino acid sequence having at least 97% identify to SEQ ID NO: 21 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 21 , or

[0619] (d) an amino acid sequence having at least 97% identify to SEQ ID NO: 22 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 22.

[0620] The nucleotide sequence encoding Six2 or a functional variant thereof may comprise:

[0621] (a) SEQ ID NO: 23,

[0622] (b) SEQ ID NO: 24,

[0623] (c) SEQ ID NO: 25,

[0624] (d) SEQ ID NO: 60, or

[0625] (d) a nucleotide sequence having at least 60% identity to SEQ ID NO: 23, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 21 , or

[0626] (e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 24, SEQ ID NO: 25 or SEQ ID NO: 60, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 22.

[0627] The nucleotide sequence encoding Six2 or a functional variant thereof may comprise a nucleic acid sequence having at least 60% identity to SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25 or SEQ ID NO: 60. The nucleotide sequence having at least 60% identity to SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25 or SEQ ID NO: 60 may have at least 70%, 75%, 80%, 85%, 90% or 95% identity to SEQ ID NO: 23, SEQ ID NO: 24, or SEQ ID NO: 25, respectively. SEQ ID NO: 23 and SEQ ID NO: 24 share 818 identical nucleotides out of 891 and thus are at least 91% identical to one another. SEQ ID NO: 24 and SEQ ID NO: 25 share 687 identical nucleotides out of 885 and therefore have at least 77% sequence identity to each other and encode the same protein sequence. SEQ ID NO: 24 and SEQ ID NO: 60 share 709 identical nucleotides out of 885 and therefore have at least 80% sequence identity to each other and encode the same protein sequence. The non-identical nucleotides may represent silent mutations (i.e. mutations which do not alter the sequence of the encoded amino acid). The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid, for example by one or more conservative amino acid mutation. The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid by up to 20, up to 15, up to 10, up to 9, up to 8, up to 7, up to 6, up to 5, up to 4, up to 3, up to 2 or up to 1 conservative amino acid mutation.

[0628] The nucleotide sequence encoding Six2 or a functional variant thereof may comprise:

[0629] (a) SEQ ID NO: 23,

[0630] (b) SEQ ID NO: 24,

[0631] (c) SEQ ID NO: 25,

[0632] (d) SEQ ID NO: 60, or

[0633] (d) a nucleotide sequence having at least 77% identity to SEQ ID NO: 23, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 21 , or (e) a nucleotide sequence having at least 80% identity to SEQ ID NO: 24, SEQ ID NO: 25 or SEQ ID NO: 60, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 22.

[0634] The nucleotide sequence encoding Six2 or a functional variant thereof may comprise:

[0635] (a) SEQ ID NO: 23,

[0636] (b) SEQ ID NO: 24,

[0637] (c) SEQ ID NO: 25,

[0638] (d) SEQ ID NO: 60, or

[0639] (d) a nucleotide sequence having at least 91 % identity to SEQ ID NO: 23, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 21 , or

[0640] (e) a nucleotide sequence having at least 91 % identity to SEQ ID NO: 24, SEQ ID NO: 25 or SEQ ID NO: 60, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 22.

[0641] The nucleic acid sequence may encode Six2. The nucleotide sequence encoding Six2 may comprise:

[0642] (a) SEQ ID NO: 23,

[0643] (b) SEQ ID NO: 24,

[0644] (c) SEQ ID NO: 25, or

[0645] (d) SEQ ID NO: 60.

[0646] The nucleic acid molecule may encode at least two transcription factors, or functional variants thereof, wherein one transcription factor is Six2 and wherein the at least two transcription factors further comprise at least one transcription factor selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl 1 , Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

[0647] According to any aspect of the invention, the transcription factors may comprise:

[0648] (a) Six2 and Pou4f3;

[0649] (b) Six2 and Gfi1 ;

[0650] (c) Six2 and Isl1 ;

[0651] (d) Six2 and Lhx3;

[0652] (e) Six2 and Pknox2; or

[0653] (f) Six2 and Kcnip3.

[0654] According to any aspect of the invention, the transcription factors may comprise:

[0655] (a) Six2, Lhx3 and Pou4f3;

[0656] (b) Six2, Gfi1 and Pou4f3;

[0657] (b) Six2, Lhx3 and Gfi1 ;

[0658] (c) Six2, Lhx3 and Isl1 ;

[0659] (d) Six2, Lhx3 and Pknox2; or

[0660] (e) Six2, Lhx3 and Kcnip3. As used herein, “Pknox2” refers to PBX / Knotted 1 Homeobox 2. In humans it is encoded by the PKNOX2 gene, also known as Homeobox Protein PKNOX2; Homeobox Protein PREP-2; PBX / Knotted Homeobox 2; and PREP2. The mouse ortholog Pknox2 is also known as Homeobox protein D230005H23Rik and Prep2. In humans, the Ensembl gene ID is ENSG00000165495. An example of a transcript is the Ensembl transcript ID ENST00000298282.14 and the UniProt ID is Q96KN3-1 ; codon-optimised and alternatively spliced transcript variants are encompassed. In mice, the Ensembl gene ID is ENSMUSG00000035934. An example of a transcript is the Ensembl transcript ID ENSMUST00000039674.13 and the UniProt ID is Q8BG99; codon-optimised and alternatively spliced transcript variants are encompassed. Functional data concerning Pknox2 in cochlear hair cell reprogramming, either alone or in combination with Atohl , has not previously been reported. WO2018 / 148071 describes Pknox2 as a “co-transcription factor” alleging that it “synergistically enhances Atohl -mediated SC-to-HC conversion” (in a list of around 50 other “cotranscription factors”) without disclosing any functional data to support this assertion.

[0661] Pknox2 may refer to the human sequence having the following amino acid sequence, identified as SEQ ID NO: 26

[0662] SEQ ID NO: 26

[0663] MMQHASPAPALTMMATQNVPPPPYQDSPQMTATAQPPSKAQAVHISAPSAAASTPVPSAPIDPQAQLEA DKRAVYRHPLFPLLTLLFEKCEQATQGSECITSASFDVDIENFVHQQEQEHKPFFSDDPELDNLMVKAIQV LRIHLLELEKVNELCKDFCNRYITCLKTKMHSDNLLRNDLGGPYSPNQPSINLHSQDLLQNSPNSMSGVS NNPQGIWPASALQQGNIAMTTVNSQWSGGALYQPVTMVTSQGQWTQAIPQGAIQIQNTQVNLDLTSL LDNEDKKSKNKRGVLPKHATNIMRSWLFQHLMHPYPTEDEKRQIAAQTNLTLLQVNNWFINARRRILQPM LDASNPDPAPKAKKIKSQHRPTQRFWPNSIAAGVLQQQGGAPGTNPDGSINLDNLQSLSSDSATMAMQQ AMMAAHDDSLDGTEEEDEDEMEEEEEEELEEEVDELQTTNVSDLGLEHSDSLE

[0664] Pknox2 may refer to the mouse sequence having the following amino acid sequence, identified as SEQ ID NO: 27

[0665] SEQ ID NO: 27

[0666] MMQHASPAPALTMMATQNVPPPPYQDSPQMTATAQPPSKAQAVHISAPSATASTPVPSAPIDPQAQLEAD KRAVYRHPLFPLLTLLFEKCEQATQGSECITSASFDVDIENFVHQQEQEHKPFFSDDPELDNLMVKAIQVL RIHLLELEKVNELCKDFCNRYITCLKTKMHSDNLLRNDLGGPYSPNQPSINLHSQDLLQNSPNSMSGVSN NPQGIWPASALQQGNIAMTTVNSQWSGGALYQPVTMVTSQGQWTQAIPQGAIQIQNTQVNLDLTSLL DNEDKKSKNKRGVLPKHATNIMRSWLFQHLMHPYPTEDEKRQIAAQTNLTLLQVNNWFINARRRILQPML DASNPDPAPKAKKIKSQHRPTQRFWPNSIAAGVLQQQGGTPGTNPDGSINLDNLQSLSSDNATMAMQQ AMMAAHDDSLDGTEEEDEDDMEEEEEEEEELEEEADELQTTNVSDLGLEHSDSLE

[0667] Pknox2 may be encoded by the following human coding sequence, identified as SEQ ID NO: 28

[0668] SEQ ID NO: 28

[0669] ATGATGCAACATGCCTCCCCAGCCCCCGCTCTGACGATGATGGCCACGCAGAATGTCCCGCCCCCA CCCTACCAGGACAGCCCACAGATGACGGCAACCGCCCAGCCACCCTCCAAGGCCCAGGCTGTCCA CATCTCTGCCCCCTCAGCTGCTGCCAGCACACCTGTGCCCAGTGCCCCCATCGACCCCCAGGCCCA

[0670] GCTGGAGGCTGACAAGCGAGCTGTATACAGGCACCCTCTTTTCCCGCTCCTGACGCTGCTGTTTGAG

[0671] AAATGTGAACAGGCCACCCAGGGCTCTGAGTGCATCACCTCCGCCAGCTTTGATGTGGACATCGAGA

[0672] ACTTTGTCCACCAGCAGGAACAGGAGCACAAACCCTTCTTCAGCGATGACCCAGAACTGGACAATCT

[0673] GATGGTGAAGGCAATCCAGGTCCTGAGAATCCACCTGCTGGAGCTGGAGAAAGTCAATGAACTCTGC

[0674] AAGGACTTTTGTAACCGTTACATCACCTGCCTCAAAACCAAGATGCACAGCGACAACCTGCTCAGGAA

[0675] TGATCTAGGGGGGCCCTACTCCCCCAACCAGCCCTCCATCAACCTTCACTCACAGGACCTCCTGCAG

[0676] AATTCCCCCAATTCCATGTCCGGAGTCTCCAATAACCCCCAGGGGATTGTGGTCCCAGCCTCAGCGC

[0677] TCCAGCAGGGCAACATCGCCATGACAACCGTCAACTCACAAGTTGTGTCAGGTGGAGCCTTATACCA

[0678] ACCGGTTACCATGGTAACCTCCCAGGGTCAGGTGGTCACCCAAGCAATCCCCCAGGGAGCCATCCA

[0679] GATCCAGAACACACAGGTTAACCTTGACCTCACCTCCCTCCTGGACAATGAGGATAAGAAGTCCAAG

[0680] AACAAACGAGGAGTCTTGCCCAAGCATGCCACCAATATAATGCGTTCTTGGCTCTTCCAGCATCTCAT

[0681] GCACCCCTACCCCACGGAGGATGAGAAGAGGCAGATCGCAGCCCAGACCAACCTCACCCTCCTGCA

[0682] AGTAAACAACTGGTTCATCAATGCCCGGAGGCGCATCCTGCAGCCCATGCTTGATGCCAGCAACCCA

[0683] GATCCTGCCCCCAAAGCCAAGAAGATCAAGTCTCAGCACCGGCCCACCCAAAGATTCTGGCCCAACT

[0684] CCATCGCTGCGGGGGTGCTGCAGCAGCAGGGCGGTGCCCCAGGGACAAACCCCGATGGTTCCATC

[0685] AACTTGGACAACCTGCAGTCCCTGTCCTCAGACAGTGCCACCATGGCCATGCAGCAGGCTATGATGG

[0686] CTGCACACGATGACTCATTGGATGGGACAGAAGAAGAGGATGAGGATGAGATGGAAGAGGAGGAGG

[0687] AGGAGGAGCTGGAGGAGGAGGTCGACGAGCTGCAGACGACAAATGTCAGCGACCTGGGCTTGGAA

[0688] CACAGTGACTCCCTGGAGTAG

[0689] Pknox2 may be encoded by the following mouse coding sequence, identified as SEQ ID NO: 29

[0690] SEQ ID NO: 29

[0691] ATGATGCAACATGCCTCCCCAGCCCCAGCTCTGACAATGATGGCCACGCAGAATGTCCCTCCCCCAC

[0692] CCTACCAGGACAGCCCCCAGATGACAGCAACTGCCCAGCCACCTTCCAAGGCCCAGGCTGTCCACA

[0693] TCTCAGCACCCTCAGCTACCGCCAGCACACCTGTGCCCAGTGCCCCCATTGATCCCCAAGCCCAGC

[0694] TGGAGGCTGACAAGCGAGCTGTGTACAGGCACCCTCTTTTCCCGCTCCTGACGCTGCTGTTTGAGA

[0695] AATGTGAACAGGCCACCCAGGGCTCCGAGTGCATCACCTCCGCCAGCTTTGATGTGGACATCGAGA

[0696] ACTTTGTCCACCAGCAGGAGCAGGAACACAAACCCTTCTTCAGCGATGACCCAGAACTGGACAATCT

[0697] GATGGTGAAGGCAATCCAGGTCCTGAGGATCCACCTGCTAGAGTTGGAGAAAGTCAATGAGCTCTGC

[0698] AAGGACTTTTGCAACCGTTACATCACCTGCCTCAAAACCAAGATGCACAGTGATAACCTGCTCAGGAA

[0699] TGACCTCGGGGGGCCCTACTCCCCCAACCAGCCCTCCATAAACCTTCACTCACAGGACCTCCTGCA

[0700] GAATTCCCCCAATTCAATGTCTGGAGTCTCCAATAACCCCCAGGGGATTGTGGTCCCAGCCTCAGCA

[0701] CTCCAGCAGGGCAACATCGCCATGACAACCGTCAATTCTCAAGTCGTGTCAGGTGGAGCCTTATATCA

[0702] GCCGGTTACCATGGTAACCTCCCAAGGTCAGGTGGTCACCCAAGCAATCCCCCAGGGAGCCATCCA

[0703] GATCCAGAATACACAGGTTAACCTTGACCTCACCTCCCTCCTGGACAATGAGGATAAGAAGTCCAAGA

[0704] ACAAACGAGGAGTCTTGCCCAAGCATGCCACCAATATAATGCGTTCTTGGCTCTTCCAGCATCTCATG

[0705] CACCCCTATCCCACTGAAGATGAGAAGAGGCAGATTGCCGCGCAGACAAACCTCACCCTTCTGCAAG

[0706] TAAACAACTGGTTCATCAATGCCAGGAGGCGCATCCTGCAGCCCATGCTTGATGCCAGCAACCCAGA

[0707] TCCTGCTCCCAAAGCCAAGAAAATCAAGTCTCAGCACCGGCCCACCCAAAGATTCTGGCCCAATTCC

[0708] ATTGCTGCTGGGGTTCTGCAACAGCAGGGTGGCACCCCAGGGACGAACCCTGATGGTTCCATCAAC TTGGACAACCTGCAGTCCCTGTCCTCAGACAATGCCACCATGGCCATGCAGCAGGCAATGATGGCTG CACATGATGATTCATTGGATGGCACGGAAGAAGAGGATGAAGATGATATGGAGGAGGAGGAAGAGGA GGAGGAGGAGCTAGAGGAGGAGGCTGATGAGCTACAGACAACGAATGTCAGCGACCTGGGCTTGG AACACAGTGACTCCCTGGAGTAG

[0709] Pknox2 may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 30

[0710] SEQ ID NO: 30

[0711] ATGATGCAGCACGCATCTCCCGCCCCTGCCCTGACCATGATGGCTACCCAGAACGTGCCCCCACCA CCATACCAGGATAGCCCACAGATGACCGCTACCGCCCAGCCCCCATCTAAGGCCCAGGCTGTGCACA TTAGCGCCCCCTCTGCCACCGCCAGCACCCCCGTGCCATCTGCTCCTATCGACCCACAGGCCCAGC TGGAAGCCGACAAAAGAGCCGTGTACAGACACCCACTGTTCCCACTGCTGACCCTGCTGTTCGAGA AGTGTGAGCAGGCCACTCAGGGCAGCGAATGTATCACCTCCGCTTCTTTCGACGTGGACATCGAGAA TTTCGTGCACCAGCAGGAACAGGAACACAAGCCATTCTTCTCCGATGACCCTGAGCTGGACAACCTG ATGGTGAAGGCCATCCAGGTCCTGAGAATTCACCTGCTGGAACTGGAGAAGGTGAACGAGCTGTGC AAGGATTTTTGCAACAGGTACATCACCTGCCTGAAGACTAAGATGCACTCTGATAATCTGCTGAGAAA CGACCTGGGAGGGCCTTATAGCCCAAATCAGCCTAGCATTAATTTGCATTCTCAGGATCTGCTCCAGA ACAGCCCTAACAGCATGTCCGGGGTGAGTAACAACCCTCAGGGGATCGTGGTGCCCGCCAGCGCTC TGCAGCAGGGCAACATCGCCATGACCACAGTGAACAGCCAGGTGGTGTCCGGCGGCGCCCTGTAC CAGCCAGTGACCATGGTGACCTCTCAGGGACAGGTGGTGACCCAGGCAATCCCCCAGGGCGCCAT CCAGATTCAGAACACCCAGGTGAATCTGGATCTGACCAGTCTGCTGGACAACGAGGACAAGAAGAGT AAGAACAAGAGGGGAGTGCTGCCCAAGCACGCTACCAACATCATGAGGTCCTGGCTGTTTCAGCATC TGATGCACCCATACCCCACCGAAGATGAAAAGCGCCAGATTGCTGCCCAGACCAACCTGACACTGCT GCAGGTGAATAACTGGTTTATCAATGCCAGACGGCGGATTCTGCAGCCTATGCTCGACGCCAGCAAC CCAGATCCTGCCCCAAAGGCCAAGAAGATCAAGAGTCAGCACAGACCCACCCAGCGATTTTGGCCC AACTCTATTGCTGCCGGAGTGCTGCAGCAGCAGGGCGGCACACCAGGCACAAACCCTGACGGCAG CATCAATCTGGACAACCTGCAGAGCCTGTCCAGCGACAATGCCACAATGGCAATGCAGCAGGCCATG ATGGCTGCACACGACGACTCCCTCGACGGTACCGAGGAGGAGGACGAGGACGATATGGAGGAGGA AGAGGAGGAGGAGGAGGAGCTGGAAGAGGAGGCTGATGAGCTGCAGACCACAAACGTGAGCGACC TGGGCCTGGAGCACTCTGACAGCCTGGAATAG

[0712] The functional variant of Pknox2 may comprise an amino acid sequence at least 70% identical to SEQ ID NO: 26 or SEQ ID NO: 27. The functional variant of Pknox2 may comprise an amino acid sequence at least 80% identical to SEQ ID NO: 26 or SEQ ID NO: 27. The functional variant of Pknox2 may comprise an amino acid sequence at least 85% identical to SEQ ID NO: 26 or SEQ ID NO: 27. The functional variant of Pknox2 may comprise an amino acid sequence at least 90% identical to SEQ ID NO: 26 or SEQ ID NO: 27. The functional variant of Pknox2 may comprise an amino acid sequence at least 95% identical to SEQ ID NO: 26 or SEQ ID NO: 27. The functional variant of Pknox2 may comprise an amino acid sequence at least 96% identical to SEQ ID NO: 26 or SEQ ID NO: 27. The functional variant of Pknox2 may comprise an amino acid sequence at least 97% identical to SEQ ID NO: 26 or SEQ ID NO: 27. The functional variant of Pknox2 may comprise an amino acid sequence at least 98% identical to SEQ ID NO: 26 or SEQ ID NO: 27. The functional variant of Pknox2 may comprise an amino acid sequence at least 99% identical to SEQ ID NO: 26 or SEQ ID NO: 27. SEQ ID NO: 26 and SEQ ID NO: 27 share 467 identical amino acids out of 474 and thus are at least 98% identical to one another. The nucleic acid sequence may comprise any nucleic acid sequence encoding a functional variant Pknox2. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 70% identical to SEQ ID NO: 26 or SEQ ID NO: 27. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 95% identical to SEQ ID NO: 26 or SEQ ID NO: 27. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 98% identical to SEQ ID NO: 26 or SEQ ID NO: 27.

[0713] The functional variant of Pknox2 may consist essentially of an amino acid sequence at least 70% identical to SEQ ID NO: 26 or SEQ ID NO: 27. The functional variant of Pknox2 may consist essentially of any amino acid sequence described elsewhere herein as a sequence that the functional variant of Pknox2 may comprise.

[0714] The nucleic acid sequence may comprise any nucleic acid sequence encoding Pknox2. Pknox2 may comprise an amino acid sequence according to SEQ ID NO: 26 or SEQ ID NO: 27. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 26 or SEQ ID NO: 27. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 26. Alternatively, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 27.

[0715] The nucleotide sequence encoding Pknox2 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0716] (a) SEQ ID NO: 26,

[0717] (b) SEQ ID NO: 27,

[0718] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 26 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 26, or

[0719] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 27 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 27.

[0720] The nucleotide sequence encoding Pknox2 or a functional variant thereof may consist essentially of a nucleic acid sequence encoding:

[0721] (a) SEQ ID NO: 26,

[0722] (b) SEQ ID NO: 27,

[0723] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 26 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 27, or

[0724] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 26 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 27. The nucleotide sequence encoding Pknox2 or a functional variant thereof may consist essentially of any nucleic acid sequence described elsewhere herein as a sequence that may encode Pknox2 or functional variant of Pknox2.

[0725] The nucleotide sequence encoding Pknox2 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0726] (a) SEQ ID NO: 26,

[0727] (b) SEQ ID NO: 27,

[0728] (c) an amino acid sequence having at least 98% identify to SEQ ID NO: 26 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 26, or

[0729] (d) an amino acid sequence having at least 98% identify to SEQ ID NO: 27 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 27.

[0730] The nucleotide sequence encoding Pknox2 or a functional variant thereof may comprise:

[0731] (a) SEQ ID NO: 28,

[0732] (b) SEQ ID NO: 29,

[0733] (c) SEQ ID NO: 30, or

[0734] (d) a nucleotide sequence having at least 60% identity to SEQ ID NO: 28, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 26, or

[0735] (e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 29 or SEQ ID NO: 30, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 27.

[0736] The nucleotide sequence encoding Pknox2 or a functional variant thereof may comprise a nucleic acid sequence having at least 60% identity to SEQ ID NO: 28, SEQ ID NO: 29, or SEQ ID NO: 30. The nucleotide sequence having at least 60% identity to SEQ ID NO: 28, SEQ ID NO: 29, or SEQ ID NO: 30 may have at least 70%, 75%, 80%, 85%, 90% or 95% identity to SEQ ID NO: 28, SEQ ID NO: 29, or SEQ ID NO: 30, respectively. SEQ ID NO: 28 and SEQ ID NO: 29 share 1345 identical nucleotides out of 1425 and thus are at least 94% identical to one another. SEQ ID NO: 29 and SEQ ID NO: 30 share 1137 identical nucleotides out of 1425 and therefore have at least 79% sequence identity to each other and encode the same protein sequence. The non-identical nucleotides may represent silent mutations (i.e. mutations which do not alter the sequence ofthe encoded amino acid). The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid, for example by one or more conservative amino acid mutation. The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid by up to 20, up to 15, up to 10, up to 9, up to 8, up to 7, up to 6, upto 5, up to 4, up to 3, up to 2 or up to 1 conservative amino acid mutation.

[0737] The nucleotide sequence encoding Pknox2 or a functional variant thereof may comprise:

[0738] (a) SEQ ID NO: 28,

[0739] (b) SEQ ID NO: 29,

[0740] (c) SEQ ID NO: 30, or (d) a nucleotide sequence having at least 79% identity to SEQ ID NO: 28, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 26, or

[0741] (e) a nucleotide sequence having at least 79% identity to SEQ ID NO: 29 or SEQ ID NO: 30, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 27.

[0742] The nucleotide sequence encoding Pknox2 or a functional variant thereof may comprise:

[0743] (a) SEQ ID NO: 28,

[0744] (b) SEQ ID NO: 29,

[0745] (c) SEQ ID NO: 30, or

[0746] (d) a nucleotide sequence having at least 94% identity to SEQ ID NO: 28, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 26, or

[0747] (e) a nucleotide sequence having at least 94% identity to SEQ ID NO: 29 or SEQ ID NO: 30, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 27.

[0748] The nucleic acid sequence may encode Pknox2. The nucleotide sequence encoding Pknox2 may comprise:

[0749] (a) SEQ ID NO: 28,

[0750] (b) SEQ ID NO: 29, or

[0751] (c) SEQ ID NO: 30.

[0752] The nucleic acid molecule may encode at least two transcription factors, or functional variants thereof, wherein one transcription factor is Pknox2 and wherein the at least two transcription factors further comprise at least one transcription factor selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

[0753] According to any aspect of the invention, the transcription factors may comprise:

[0754] (a) Pknox2 and Pou4f3;

[0755] (b) Pknox2 and Gfi1 ;

[0756] (c) Pknox2 and Lhx3;

[0757] (d) Pknox2 and Isl1 ;

[0758] (e) Pknox2 and Six2; or

[0759] (f) Pknox2 and Kcnip3.

[0760] According to any aspect of the invention, the transcription factors may comprise:

[0761] (a) Pknox2, Kcnip3 and Pou4f3;

[0762] (b) Pknox2, Kcnip3 and Gfi1 ;

[0763] (c) Pknox2, Kcnip3 and Lhx3;

[0764] (d) Pknox2, Kcnip3 and Isl1 ; or

[0765] (e) Pknox2, Kcnip3 and Six2. According to an alternative statement of the first aspect, the invention provides a nucleic acid molecule encoding at least two transcription factors, or functional variants thereof, wherein one transcription factor is Pknox2 and wherein the at least two transcription factors further comprise at least one transcription factor selected from the group consisting of Gfi1 and Kcnip3. According to this alternative statement of the first aspect, the nucleic acid molecule may further encode Atohl , or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pknox2, Atohl and one or more of Gfi1 and Kcnip3, or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pknox2, Atohl and one or more of Gfi1 and Kcnip3.

[0766] As used herein, “Kcnip3” refers to Potassium Voltage-Gated Channel Interacting Protein 3, also known as Calsenilin. In humans it is encoded by the KCNIP3 gene, also known as CSEN, DREAM and KCHIP3. The mouse ortholog Kcnip3 is also known as 4933407H12Rik, Csen, DREAM, KChlP3 and R74849. In humans, the Ensembl gene ID is ENSG00000115041 . An example of a transcript is the Ensembl transcript ID ENST00000468529.1 and the UniProt ID is Q9Y2W7-3; codon-optimised and alternatively spliced transcript variants are encompassed. In mice, the Ensembl gene ID is ENSMUSG00000079056. An example of a transcript is the Ensembl transcript ID ENSMUST00000088538.6 and the UniProt ID is Q3YAA9; codon-optimised and alternatively spliced transcript variants are encompassed. It is thought that Kcnip3 has not previously been proposed to have a role in cochlear hair cell reprogramming, either alone or in combination with Atohl .

[0767] Kcnip3 may refer to the human sequence having the following amino acid sequence, identified as SEQ ID NO: 31

[0768] SEQ ID NO: 31

[0769] MGIQGMELCAMAVVVLLFIAVLKQFGILEPISMEDSSDSELELSTVRHQPEGLDQLQAQTKFTKKELQSLY RGFKNECPTGLVDEDTFKLIYAQFFPQGDATTYAHFLFNAFDADGNGAIHFEDFVVGLSILLRGTVHEKLK WAFNLYDINKDGYITKEEMLAIMKSIYDMMGRHTYPILREDAPAEHVERFFEKMDRNQDGWTIEEFLEAC QKDENIMSSMQLFENVI

[0770] Kcnip3 may refer to the mouse sequence having the following amino acid sequence, identified as SEQ ID NO: 32

[0771] SEQ ID NO: 32

[0772] MGIQGMELCAMAVVVLLFIAVLKQFGILEPMSMEDSSDSELELSTVRHQPEGLDQLQAQTKFTKKELQSL YRGFKNECPTGLVDEDTFKLIYSQFFPQGDATTYAHFLFNAFDADGNGAIHFEDFVVGLSILLRGTVHEKL KWAFNLYDINKDGCITKEEMLAIMKSIYDMMGRHTYPILREDAPLEHVERFFQKMDRNQDGWTIDEFLET CQKDENIMNSMQLFENVI

[0773] Kcnip3 may be encoded by the following human coding sequence, identified as SEQ ID NO: 33

[0774] SEQ ID NO: 33 ATGGGCATCCAGGGCATGGAGCTGTGCGCCATGGCCGTGGTGGTGCTGCTGTTCATCGCCGTCCTC

[0775] AAGCAGTTCGGCATCCTGGAGCCCATATCCATGGAAGATAGCAGCGACAGTGAGCTGGAGCTGTCCA

[0776] CGGTGCGCCACCAGCCAGAGGGGCTGGACCAGCTGCAGGCCCAGACCAAGTTCACCAAGAAGGAG

[0777] CTGCAGTCTCTCTACAGGGGCTTTAAGAATGAGTGTCCCACGGGCCTGGTGGACGAAGACACCTTCA

[0778] AACTCATTTACGCGCAGTTCTTCCCTCAGGGAGATGCCACCACCTATGCACACTTCCTCTTCAACGCC

[0779] TTTGATGCGGACGGGAACGGGGCCATCCACTTTGAGGACTTTGTGGTTGGCCTCTCCATCCTGCTGC

[0780] GGGGCACAGTCCACGAGAAGCTCAAGTGGGCCTTTAATCTCTACGACATTAACAAGGATGGCTACAT

[0781] CACCAAAGAGGAGATGCTGGCCATCATGAAGTCCATCTATGACATGATGGGCCGCCACACCTACCCC

[0782] ATCCTGCGGGAGGACGCGCCGGCGGAGCACGTGGAGAGGTTCTTCGAGAAAATGGACCGGAACCA

[0783] GGATGGGGTAGTGACCATTGAAGAGTTCCTGGAGGCCTGTCAGAAGGATGAGAACATCATGAGCTCC

[0784] ATGCAGCTGTTTGAGAATGTCATCTAG

[0785] Kcnip3 may be encoded by the following mouse coding sequence, identified as SEQ ID NO: 34

[0786] SEQ ID NO: 34

[0787] ATGGGGATTCAGGGTATGGAGCTGTGCGCCATGGCTGTGGTGGTGCTGCTGTTCATTGCCGTCCTCA

[0788] AGCAGTTCGGCATCTTGGAACCCATGTCCATGGAAGACAGCAGTGACAGTGAACTGGAGTTATCCAC

[0789] GGTGCGCCATCAGCCAGAGGGCTTGGACCAGCTACAAGCTCAGACCAAGTTCACCAAGAAGGAGCT

[0790] GCAGTCCCTTTACCGAGGCTTCAAGAATGAGTGTCCCACAGGCCTGGTGGATGAAGACACCTTCAAA

[0791] CTCATTTATTCCCAGTTCTTCCCTCAGGGAGATGCCACCACCTATGCACACTTCCTCTTCAATGCCTTC

[0792] GATGCTGATGGGAACGGGGCCATCCACTTTGAGGACTTTGTGGTTGGGCTCTCCATCCTGCTTCGAG

[0793] GGACGGTCCATGAGAAGCTCAAGTGGGCCTTCAATCTCTATGACATTAACAAGGATGGTTGCATCACC

[0794] AAGGAGGAGATGCTGGCCATCATGAAGTCCATCTACGACATGATGGGCCGCCACACCTACCCCATCC

[0795] TGCGGGAGGATGCACCCCTGGAGCATGTGGAGAGGTTCTTTCAGAAAATGGACAGGAACCAGGATG

[0796] GAGTGGTGACCATTGATGAATTTCTGGAGACTTGTCAGAAGGATGAGAACATCATGAACTCCATGCAG

[0797] CTGTTTGAGAACGTCATCTAG

[0798] Kcnip3 may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 35

[0799] SEQ ID NO: 35

[0800] ATGGGAATCCAGGGCATGGAGCTGTGTGCCATGGCCGTAGTGGTGCTGCTGTTCATCGCCGTGCTG

[0801] AAGCAGTTCGGCATCCTGGAACCAATGTCTATGGAGGATTCATCCGACAGCGAGCTGGAGCTCTCCA

[0802] CCGTGCGCCACCAGCCTGAGGGGCTGGATCAGCTCCAGGCTCAGACCAAGTTTACCAAGAAGGAGC

[0803] TTCAGTCACTGTATCGGGGCTTCAAGAACGAGTGCCCCACCGGCCTGGTGGATGAGGATACCTTCAA

[0804] ACTGATCTACAGCCAGTTCTTCCCCCAGGGCGATGCTACAACTTACGCCCACTTCCTGTTCAATGCCT

[0805] TCGACGCCGACGGCAACGGCGCCATTCACTTTGAAGATTTCGTGGTGGGGCTGTCAATCCTCCTGA

[0806] GGGGCACTGTCCACGAGAAGCTGAAGTGGGCATTCAACCTGTACGACATCAACAAGGATGGGTGCA

[0807] TCACTAAGGAGGAGATGCTGGCCATCATGAAGAGTATCTACGACATGATGGGGAGGCACACCTACCC

[0808] AATCCTGAGGGAAGACGCTCCGCTGGAACACGTCGAACGCTTCTTCCAGAAGATGGATAGAAATCAG

[0809] GACGGCGTGGTGACCATTGATGAGTTCCTGGAGACCTGCCAGAAGGACGAGAACATCATGAATAGCA

[0810] TGCAGCTGTTCGAGAACGTGATCTGA The functional variant of Kcnip3 may comprise an amino acid sequence at least 70% identical to SEQ ID NO: 31 or SEQ ID NO: 32. The functional variant of Kcnip3 may comprise an amino acid sequence at least 80% identical to SEQ ID NO: 31 or SEQ ID NO: 32. The functional variant of Kcnip3 may comprise an amino acid sequence at least 85% identical to SEQ ID NO: 31 or SEQ ID NO: 32. The functional variant of Kcnip3 may comprise an amino acid sequence at least 90% identical to SEQ ID NO: 31 or SEQ ID NO: 32. The functional variant of Kcnip3 may comprise an amino acid sequence at least 95% identical to SEQ ID NO: 31 or SEQ ID NO: 32. The functional variant of Kcnip3 may comprise an amino acid sequence at least 96% identical to SEQ ID NO: 31 or SEQ ID NO: 32. The functional variant of Kcnip3 may comprise an amino acid sequence at least 97% identical to SEQ ID NO: 31 or SEQ ID NO: 32. The functional variant of Kcnip3 may comprise an amino acid sequence at least 98% identical to SEQ ID NO: 31 or SEQ ID NO: 32. The functional variant of Kcnip3 may comprise an amino acid sequence at least 99% identical to SEQ ID NO: 31 or SEQ ID NO: 32. SEQ ID NO: 31 and SEQ ID NO: 32 share 222 identical amino acids out of 230 and thus are at least 96% identical to one another. The nucleic acid sequence may comprise any nucleic acid sequence encoding a functional variant Kcnip3. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 70% identical to SEQ ID NO: 31 or SEQ ID NO: 32. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 95% identical to SEQ ID NO: 31 or SEQ ID NO: 32. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 96% identical to SEQ ID NO: 31 or SEQ ID NO: 32.

[0811] The functional variant of Kcnip3 may consist essentially of an amino acid sequence at least 70% identical to SEQ ID NO: 31 or SEQ ID NO: 32. The functional variant of Kcnip3 may consist essentially of any amino acid sequence described elsewhere herein as a sequence that the functional variant of Kcnip3 may comprise.

[0812] The nucleic acid sequence may comprise any nucleic acid sequence encoding Kcnip3. Kcnip3 may comprise an amino acid sequence according to SEQ ID NO: 31 or SEQ ID NO: 32. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 31 or SEQ ID NO: 32. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 31 . Alternatively, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 32.

[0813] The nucleotide sequence encoding Kcnip3 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0814] (a) SEQ ID NO: 31 ,

[0815] (b) SEQ ID NO: 32,

[0816] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 31 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 31 , or

[0817] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 32 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 32. The nucleotide sequence encoding Kcnip3 or a functional variant thereof may consist essentially of a nucleic acid sequence encoding:

[0818] (a) SEQ ID NO: 31 ,

[0819] (b) SEQ ID NO: 32,

[0820] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 31 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 31 , or

[0821] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 32 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 32.

[0822] The nucleotide sequence encoding Kcnip3 or a functional variant thereof may consist essentially of any nucleic acid sequence described elsewhere herein as a sequence that may encode Kcnip3 or functional variant of Kcnip3.

[0823] The nucleotide sequence encoding Kcnip3 or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0824] (a) SEQ ID NO: 31 ,

[0825] (b) SEQ ID NO: 32,

[0826] (c) an amino acid sequence having at least 96% identify to SEQ ID NO: 31 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 31 , or

[0827] (d) an amino acid sequence having at least 96% identify to SEQ ID NO: 32 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 32.

[0828] The nucleotide sequence encoding Kcnip3 or a functional variant thereof may comprise:

[0829] (a) SEQ ID NO: 33,

[0830] (b) SEQ ID NO: 34,

[0831] (c) SEQ ID NO: 35, or

[0832] (d) a nucleotide sequence having at least 60% identity to SEQ ID NO: 33, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 31 , or

[0833] (e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 34 or SEQ ID NO: 35, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 32.

[0834] The nucleotide sequence encoding Kcnip3 or a functional variant thereof may comprise a nucleic acid sequence having at least 60% identity to SEQ ID NO: 33, SEQ ID NO: 34, or SEQ ID NO: 35. The nucleotide sequence having at least 60% identity to SEQ ID NO: 33, SEQ ID NO: 34, or SEQ ID NO: 35 may have at least 70%, 75%, 80%, 85%, 90% or 95% identity to SEQ ID NO: 33, SEQ ID NO: 34, or SEQ ID NO: 35, respectively. SEQ ID NO: 33 and SEQ ID NO: 34 share 630 identical nucleotides out of 693 and thus are at least 90% identical to one another. SEQ ID NO: 34 and SEQ ID NO: 35 share 576 identical nucleotides out of 693 and therefore have at least 83% sequence identity to each other and encode the same protein sequence. The non-identical nucleotides may represent silent mutations (i.e. mutations which do not alter the sequence ofthe encoded amino acid). The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid, for example by one or more conservative amino acid mutation. The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid by up to 20, up to 15, up to 10, up to 9, up to 8, up to 7, up to 6, upto 5, up to 4, up to 3, up to 2 or up to 1 conservative amino acid mutation.

[0835] The nucleotide sequence encoding Kcnip3 or a functional variant thereof may comprise:

[0836] (a) SEQ ID NO: 33,

[0837] (b) SEQ ID NO: 34,

[0838] (c) SEQ ID NO: 35, or

[0839] (d) a nucleotide sequence having at least 83% identity to SEQ ID NO: 33, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 31 , or

[0840] (e) a nucleotide sequence having at least 83% identity to SEQ ID NO: 34 or SEQ ID NO: 35, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 32.

[0841] The nucleotide sequence encoding Kcnip3 or a functional variant thereof may comprise:

[0842] (a) SEQ ID NO: 33,

[0843] (b) SEQ ID NO: 34,

[0844] (c) SEQ ID NO: 35, or

[0845] (d) a nucleotide sequence having at least 94% identity to SEQ ID NO: 33, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 31 , or

[0846] (e) a nucleotide sequence having at least 94% identity to SEQ ID NO: 34 or SEQ ID NO: 35, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 32.

[0847] The nucleic acid sequence may encode Kcnip3. The nucleotide sequence encoding Kcnip3 may comprise:

[0848] (a) SEQ ID NO: 33,

[0849] (b) SEQ ID NO: 34, or

[0850] (c) SEQ ID NO: 35.

[0851] The nucleic acid molecule may encode at least two transcription factors, or functional variants thereof, wherein one transcription factor is Kcnip3 and wherein the at least two transcription factors further comprise at least one transcription factor selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2 and Pknox2, wherein the at least two transcription factors do not comprise Atohl .

[0852] According to any aspect of the invention, the transcription factors may comprise:

[0853] (a) Kcnip3 and Pou4f3;

[0854] (b) Kcnip3 and Gfi1 ;

[0855] (c) Kcnip3 and Lhx3;

[0856] (d) Kcnip3 and Isl1 ;

[0857] (e) Kcnip3 and Six2; or

[0858] (f) Kcnip3 and Pknox2. According to any aspect of the invention, the transcription factors may comprise:

[0859] (a) Kcnip3, Pknox2 and Pou4f3;

[0860] (b) Kcnip3, Pknox2 and Gfi1 ;

[0861] (c) Kcnip3, Pknox2 and Lhx3;

[0862] (d) Kcnip3, Pknox2 and Isl1 ; or

[0863] (e) Kcnip3, Pknox2 and Six2.

[0864] According to any aspect of the invention, the transcription factors may comprise:

[0865] (a) Kcnip3, Isl1 and Pou4f3;

[0866] (b) Kcnip3, Isl1 and Gfi1 ;

[0867] (c) Kcnip3, Isl1 and Lhx3;

[0868] (d) Kcnip3, Isl1 and Six2; or

[0869] (e) Kcnip3, Isl1 and Pknox2.

[0870] According to an alternative statement of the first aspect, the invention provides a nucleic acid molecule encoding at least two transcription factors, or functional variants thereof, wherein one transcription factor is Kcnip3 and wherein the at least two transcription factors further comprise at least one transcription factor selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl1 , Six2 and Pknox2.

[0871] According to an alternative statement of the first aspect, the invention provides a nucleic acid molecule encoding Kcnip3, or a functional variant thereof, under the control of promoter for expression of Kcnip3 in cochlear cells. The nucleic acid molecule may be recombinant and / or isolated. The promoter may be selective for or specific for cochlear cells.

[0872] According to the alternative statements of the first aspect wherein the nucleic acid molecule encodes Kcnip3, the nucleic acid molecule may further encode Atohl or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Kcnip3 and Atohl .

[0873] As used herein, ‘ tohl ” refers to atonal bHLH transcription factor 1 . In humans it is encoded by the ATOH1 gene, also known as BHLHA14, HATH1 , MATH-1 , MATH1. The mouse ortholog Atohl is also known as atonal bHLH transcription factor 1 , Hathl , Mathl and bHLHa14. In humans, the Ensembl gene ID is ENSG00000172238. An example of a transcript is the Ensembl transcript ID ENST00000306011 .6 and the UniProt ID is Q92858; codon-optimised and alternatively spliced transcript variants are encompassed. In mice, the Ensembl gene ID is ENSMUSG00000073043. An example of a transcript is the Ensembl transcript ID ENSMUST00000101351 .6 and the UniProt ID is P48985; codon-optimised and alternatively spliced transcript variants are encompassed.

[0874] The transcription factors according to the present invention do not comprise Atohl . The transcription factors may not comprise Atohl or a functional variant thereof. The transcription factors may not comprise an atonal-associated factor. The transcription factors may not comprise an atonal-associated factor, or a functional variant thereof. Atonal-associated factors are further described in WO 2000 / 73764, incorporated herein by reference.

[0875] The nucleic acid molecule, system, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any aspect of the invention may be defined as not comprising, encoding, targeting, introducing or increasing the expression of Atohl , as applicable. The nucleic acid molecule, system, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any aspect of the invention may be defined as not comprising, encoding, targeting, introducing or increasing the expression of Atohl or a functional variant thereof, as applicable. The nucleic acid molecule, system, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any aspect of the invention may be defined as not comprising, encoding, targeting, introducing or increasing the expression of an atonal-associated factor, as applicable. The nucleic acid molecule, system, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any aspect of the invention may be defined as not comprising, encoding, targeting, introducing or increasing the expression of an atonal-associated factor, or a functional variant thereof, as applicable.

[0876] Atohl may refer to the human sequence having the following amino acid sequence, identified as SEQ ID NO: 36

[0877] SEQ ID NO: 36

[0878] MSRLLHAEEWAEVKELGDHHRQPQPHHLPQPPPPPQPPATLQAREHPVYPPELSLLDSTDPRAWLAPTL QGICTARAAQYLLHSPELGASEAAAPRDEVDGRGELVRRSSGGASSSKSPGPVKVREQLCKLKGGVVVD ELGCSRQRAPSSKQVNGVQKQRRLAANARERRRMHGLNHAFDQLRNVIPSFNNDKKLSKYETLQMAQI YINALSELLQTPSGGEQPPPPPASCKSDHHHLRTAASYEGGAGNATAAGAQQASGGSQRPTPPGSCRT RFSAPASAGGYSVQLDALHFSTFEDSALTAMMAQKNLSPSLPGSILQPVQEENSKTSPRSHRSDGEFSP HSHYSDSDEAS

[0879] Atohl may refer to the mouse sequence having the following amino acid sequence, identified as SEQ ID NO: 37

[0880] SEQ ID NO: 37

[0881] MSRLLHAEEWAEVKELGDHHRHPQPHHVPPLTPQPPATLQARDLPVYPAELSLLDSTDPRAWLTPTLQG LCTARAAQYLLHSPELGASEAAAPRDEADSQGELVRRSGCGGLSKSPGPVKVREQLCKLKGGVVVDEL GCSRQRAPSSKQVNGVQKQRRLAANARERRRMHGLNHAFDQLRNVIPSFNNDKKLSKYETLQMAQIYIN ALSELLQTPNVGEQPPPPTASCKNDHHHLRTASSYEGGAGASAVAGAQPAPGGGPRPTPPGPCRTRFS GPASSGGYSVQLDALHFPAFEDRALTAMMAQKDLSPSLPGGILQPVQEDNSKTSPRSHRSDGEFSPHSH YSDSDEAS

[0882] Atohl may be encoded by the following human coding sequence, identified as SEQ ID NO: 38

[0883] SEQ ID NO: 38 ATGTCCCGCCTGCTGCATGCAGAAGAGTGGGCTGAAGTGAAGGAGTTGGGAGACCACCATCGCCAG

[0884] CCCCAGCCGCATCATCTCCCGCAACCGCCGCCGCCGCCGCAGCCACCTGCAACTTTGCAGGCGAG

[0885] AGAGCATCCCGTCTACCCGCCTGAGCTGTCCCTCCTGGACAGCACCGACCCACGCGCCTGGCTGG

[0886] CTCCCACTTTGCAGGGCATCTGCACGGCACGCGCCGCCCAGTATTTGCTACATTCCCCGGAGCTGG

[0887] GTGCCTCAGAGGCCGCTGCGCCCCGGGACGAGGTGGACGGCCGGGGGGAGCTGGTAAGGAGGAG

[0888] CAGCGGCGGTGCCAGCAGCAGCAAGAGCCCCGGGCCGGTGAAAGTGCGGGAACAGCTGTGCAAG

[0889] CTGAAAGGCGGGGTGGTGGTAGACGAGCTGGGCTGCAGCCGCCAACGGGCCCCTTCCAGCAAACA

[0890] GGTGAATGGGGTGCAGAAGCAGAGACGGCTAGCAGCCAACGCCAGGGAGCGGCGCAGGATGCATG

[0891] GGCTGAACCACGCCTTCGACCAGCTGCGCAATGTTATCCCGTCGTTCAACAACGACAAGAAGCTGTC

[0892] CAAATATGAGACCCTGCAGATGGCCCAAATCTACATCAACGCCTTGTCCGAGCTGCTACAAACGCCCA

[0893] GCGGAGGGGAACAGCCACCGCCGCCTCCAGCCTCCTGCAAAAGCGACCACCACCACCTTCGCACC

[0894] GCGGCCTCCTATGAAGGGGGCGCGGGCAACGCGACCGCAGCTGGGGCTCAGCAGGCTTCCGGAG

[0895] GGAGCCAGCGGCCGACCCCGCCCGGGAGTTGCCGGACTCGCTTCTCAGCCCCAGCTTCTGCGGGA

[0896] GGGTACTCGGTGCAGCTGGACGCTCTGCACTTCTCGACTTTCGAGGACAGCGCCCTGACAGCGATG

[0897] ATGGCGCAAAAGAATTTGTCTCCTTCTCTCCCCGGGAGCATCTTGCAGCCAGTGCAGGAGGAAAACA

[0898] GCAAAACTTCGCCTCGGTCCCACAGAAGCGACGGGGAATTTTCCCCCCATTCCCATTACAGTGACTC GGATGAGGCAAGTTAG

[0899] Atohl may be encoded by the following mouse coding sequence, identified as SEQ ID NO: 39

[0900] SEQ ID NO: 39

[0901] ATGTCCCGCCTGCTGCATGCAGAAGAGTGGGCTGAGGTAAAAGAGTTGGGGGACCACCATCGCCAT

[0902] CCCCAGCCGCACCACGTCCCGCCGCTGACGCCACAGCCACCTGCTACCCTGCAGGCGAGAGACCT

[0903] TCCCGTCTACCCGGCAGAACTGTCCCTCCTGGATAGCACCGACCCACGCGCCTGGCTGACTCCCAC

[0904] TTTGCAGGGCCTCTGCACGGCACGCGCCGCCCAGTATCTGCTGCATTCTCCCGAGCTGGGTGCCTC

[0905] CGAGGCCGCGGCGCCCCGGGACGAGGCTGACAGCCAGGGTGAGCTGGTAAGGAGAAGCGGCTGT

[0906] GGCGGCCTCAGCAAGAGCCCCGGGCCCGTCAAAGTACGGGAACAGCTGTGCAAGCTGAAGGGTGG

[0907] GGTTGTAGTGGACGAGCTTGGCTGCAGCCGCCAGCGAGCCCCTTCCAGCAAACAGGTGAATGGGG

[0908] TACAGAAGCAAAGGAGGCTGGCAGCAAACGCAAGGGAACGGCGCAGGATGCACGGGCTGAACCAC

[0909] GCCTTCGACCAGCTGCGCAACGTTATCCCGTCCTTCAACAACGACAAGAAGCTGTCCAAATATGAGA

[0910] CCCTACAGATGGCCCAGATCTACATCAACGCTCTGTCGGAGTTGCTGCAGACTCCCAATGTCGGAGA

[0911] GCAACCGCCGCCGCCCACAGCTTCCTGCAAAAATGACCACCATCACCTTCGCACCGCCTCCTCCTAT

[0912] GAAGGAGGTGCGGGCGCCTCTGCGGTAGCTGGGGCTCAGCCAGCCCCGGGAGGGGGCCCGAGAC

[0913] CTACCCCGCCCGGGCCTTGCCGGACTCGCTTCTCAGGCCCAGCTTCCTCTGGGGGTTACTCGGTGC

[0914] AGCTGGACGCTTTGCACTTCCCAGCCTTCGAGGACAGGGCCCTAACAGCGATGATGGCACAGAAGG

[0915] ACCTGTCGCCTTCGCTGCCCGGGGGCATCCTGCAGCCTGTACAGGAGGACAACAGCAAAACATCTC

[0916] CCAGATCCCACAGAAGTGACGGAGAGTTTTCCCCCCACTCTCATTACAGTGACTCTGATGAGGCCAG TTAG

[0917] Atohl may be encoded by the following codon optimised mouse sequence, identified as SEQ ID NO: 40

[0918] SEQ ID NO: 40 ATGTCTCGTTTGTTGCACGCAGAAGAATGGGCCGAAGTCAAGGAACTGGGCGATCATCACCGGCAC CCACAACCTCATCATGTGCCCCCTTTGACCCCGCAACCCCCAGCAACATTGCAAGCCCGGGATCTGC CGGTTTATCCCGCCGAGTTGTCTCTGCTAGACAGTACTGATCCTAGGGCTTGGCTCACCCCTACGCT GCAAGGACTTTGTACCGCCAGGGCTGCTCAATACCTCTTGCACAGTCCTGAATTGGGCGCTTCTGAA GCTGCCGCCCCTCGTGATGAAGCGGATTCACAAGGGGAACTAGTCAGACGCTCAGGGTGCGGTGGT TTGAGTAAATCACCTGGACCAGTTAAGGTGAGAGAGCAACTCTGTAAACTCAAAGGCGGAGTGGTGG TAGATGAACTCGGATGTAGTAGGCAACGTGCACCCAGCTCAAAGCAAGTAAACGGTGTCCAGAAACA GCGCCGACTTGCTGCTAATGCCCGCGAGAGGCGACGAATGCATGGACTGAATCATGCTTTTGATCAA CTCAGGAATGTCATACCCTCATTCAATAATGATAAGAAGCTATCTAAGTACGAAACTTTGCAAATGGCAC AAATTTATATAAATGCCCTTAGCGAACTGCTCCAAACACCAAACGTTGGTGAACAGCCTCCTCCACCTA CTGCAAGTTGTAAGAACGATCATCACCATCTGCGGACAGCTAGCTCTTACGAGGGTGGGGCCGGTGC ATCAGCCGTGGCAGGCGCGCAACCCGCTCCTGGTGGCGGACCACGTCCCACTCCCCCAGGACCCT GTAGAACCAGGTTTTCTGGGCCCGCCTCATCCGGTGGCTATTCCGTTCAACTAGATGCCTTGCATTTT CCGGCTTTTGAAGATCGGGCTCTGACCGCAATGATGGCTCAGAAAGATTTGTCTCCATCATTGCCAG GCGGTATACTCCAACCAGTTCAAGAAGATAATAGTAAGACTTCACCACGGAGTCATCGCTCCGATGGG GAATTCAGCCCACATTCACACTATTCTGATTCCGACGAAGCGTCTTAA

[0919] The functional variant of Atohl may comprise an amino acid sequence at least 70% identical to SEQ ID NO: 36 or SEQ ID NO: 37. The functional variant of Atohl may comprise an amino acid sequence at least 80% identical to SEQ ID NO: 36 or SEQ ID NO: 37. The functional variant of Atohl may comprise an amino acid sequence at least 85% identical to SEQ ID NO: 36 or SEQ ID NO: 37. The functional variant of Atohl may comprise an amino acid sequence at least 90% identical to SEQ ID NO: 36 or SEQ ID NO: 37. The functional variant of Atohl may comprise an amino acid sequence at least 95% identical to SEQ ID NO: 36 or SEQ ID NO: 37. The functional variant of Atohl may comprise an amino acid sequence at least 96% identical to SEQ ID NO: 36 or SEQ ID NO: 37. The functional variant of Atohl may comprise an amino acid sequence at least 97% identical to SEQ ID NO: 36 or SEQ ID NO: 37. The functional variant of Atohl may comprise an amino acid sequence at least 98% identical to SEQ ID NO: 36 or SEQ ID NO: 37. The functional variant of Atohl may comprise an amino acid sequence at least 99% identical to SEQ ID NO: 36 or SEQ ID NO: 37. SEQ ID NO: 36 and SEQ ID NO: 37 share 313 identical amino acids out of 354 and thus are at least 88% identical to one another. The nucleic acid sequence may comprise any nucleic acid sequence encoding a functional variant Atohl . Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 70% identical to SEQ ID NO: 36 or SEQ ID NO: 37. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 95% identical to SEQ ID NO: 36 or SEQ ID NO: 37. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding an amino acid sequence at least 97% identical to SEQ ID NO: 36 or SEQ ID NO: 37.

[0920] The nucleic acid sequence may comprise any nucleic acid sequence encoding Atohl . Atohl may comprise an amino acid sequence according to SEQ ID NO: 36 or SEQ ID NO: 37. Therefore, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 36 or SEQ ID NO: 37. For example, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 36. Alternatively, the nucleic acid sequence may comprise any nucleic acid sequence encoding SEQ ID NO: 37.

[0921] The nucleotide sequence encoding Atohl or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0922] (a) SEQ ID NO: 36,

[0923] (b) SEQ ID NO: 37,

[0924] (c) an amino acid sequence having at least 70% identify to SEQ ID NO: 36 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 36, or

[0925] (d) an amino acid sequence having at least 70% identify to SEQ ID NO: 37 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 37.

[0926] The nucleotide sequence encoding Atohl or a functional variant thereof may comprise a nucleic acid sequence encoding:

[0927] (a) SEQ ID NO: 36,

[0928] (b) SEQ ID NO: 37,

[0929] (c) an amino acid sequence having at least 88% identify to SEQ ID NO: 36 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 36, or

[0930] (d) an amino acid sequence having at least 88% identify to SEQ ID NO: 37 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 37.

[0931] The nucleotide sequence encoding Atohl or a functional variant thereof may comprise:

[0932] (a) SEQ ID NO: 38,

[0933] (b) SEQ ID NO: 39,

[0934] (c) SEQ ID NO: 40, or

[0935] (d) a nucleotide sequence having at least 60% identity to SEQ ID NO: 38, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 36, or

[0936] (e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 39 or SEQ ID NO: 40, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 37.

[0937] The nucleotide sequence encoding Atohl or a functional variant thereof may comprise a nucleic acid sequence having at least 60% identity to SEQ ID NO: 38, SEQ ID NO: 39, or SEQ ID NO: 40. The nucleotide sequence having at least 60% identity to SEQ ID NO: 38, SEQ ID NO: 39, or SEQ ID NO: 40 may have at least 70%, 75%, 80%, 85%, 90% or 95% identity to SEQ ID NO: 38, SEQ ID NO: 39, or SEQ ID NO: 40, respectively. SEQ ID NO: 38 and SEQ ID NO: 39 share 912 identical nucleotides out of 1065 and thus are at least 85% identical to one another. SEQ ID NO: 39 and SEQ ID NO: 40 share 705 identical nucleotides out of 1056 and therefore have at least 66% sequence identity to each other and encode the same protein sequence. The non-identical nucleotides may represent silent mutations (i.e. mutations which do not alter the sequence ofthe encoded amino acid). The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid, for example by one or more conservative amino acid mutation. The non-identical nucleotides may alter the amino acid sequence of the encoded amino acid by up to 20, up to 15, up to 10, up to 9, up to 8, up to 7, up to 6, up to 5, up to 4, up to 3, up to 2 or up to 1 conservative amino acid mutation.

[0938] The nucleotide sequence encoding Atohl or a functional variant thereof may comprise:

[0939] (a) SEQ ID NO: 38,

[0940] (b) SEQ ID NO: 39,

[0941] (c) SEQ ID NO: 40,

[0942] (d) a nucleotide sequence having at least 66% identity to SEQ ID NO: 38, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 36, or

[0943] (e) a nucleotide sequence having at least 66% identity to SEQ ID NO: 39 or SEQ ID NO: 40, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 37.

[0944] The nucleotide sequence encoding Atohl or a functional variant thereof may comprise:

[0945] (a) SEQ ID NO: 38,

[0946] (b) SEQ ID NO: 39,

[0947] (c) SEQ ID NO: 40,

[0948] (d) a nucleotide sequence having at least 85% identity to SEQ ID NO: 38, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 36, or

[0949] (e) a nucleotide sequence having at least 85% identity to SEQ ID NO: 39 or SEQ ID NO: 40, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 37.

[0950] The nucleic acid sequence may encode Atohl . The nucleotide sequence encoding Atohl may comprise:

[0951] (a) SEQ ID NO: 38,

[0952] (b) SEQ ID NO: 39, or

[0953] (c) SEQ ID NO: 40.

[0954] In alternative statements of the invention described elsewhere herein, Atohl or a functional variant thereof may be defined in accordance with any one or more of the statements concerning Atohl herein.

[0955] According to any aspect of the invention, the transcription factors may comprise:

[0956] (a) Pou4f3 and Gfi1 ;

[0957] (b) Gfi1 and Lhx3;

[0958] (c) Gfi1 and Six2;

[0959] (d) Lhx3 and Six2;

[0960] (e) Isl1 and Kcnip3;

[0961] (f) Pknox2 and Kcnip3;

[0962] (g) Pou4f3, Gfi1 and Kcnip3;

[0963] (h) Pou4f3, Gfi1 and Lhx3;

[0964] (I) Pou4f3, Gfi1 and Six2; 0) Pou4f3, Gfi1 , Lhx3 and Six2;

[0965] (k) Pou4f3, Gfi1 , Isl1 and Kcnip3; or

[0966] (l) Pou4f3, Gfi1 , Pknox2 and Kcnip3.

[0967] According to any aspect of the invention, the transcription factors may comprise:

[0968] (a) Pou4f3 and Gfi1 ;

[0969] (b) Gfi1 and Lhx3;

[0970] (c) Gfi1 and Six2;

[0971] (d) Gfi1 , Lhx3 and Six2;

[0972] (e) Pou4f3, Gfi1 and Lhx3;

[0973] (f) Pou4f3, Gfi1 and Six2; or

[0974] (g) Pou4f3, Gfi1 , Lhx3 and Six2.

[0975] According to any aspect of the invention, the transcription factors may comprise:

[0976] (a) Pou4f3 and Gfi1 ;

[0977] (b) Gfi1 and Lhx3;

[0978] (c) Gfi1 and Six2;

[0979] (d) Gfi1 , Lhx3 and Six2;

[0980] (e) Pou4f3, Gfi1 and Lhx3;

[0981] (f) Pou4f3, Gfi1 and Six2; or

[0982] (g) Pou4f3, Gfi1 , Lhx3 and Six2.

[0983] According to any aspect of the invention, the transcription factors may comprise or consist of Pou4f3 and Gfi1.

[0984] According to any aspect of the invention, the transcription factors may comprise or consist of Gfi1 and Lhx3.

[0985] According to any aspect of the invention, the transcription factors may comprise or consist of Gfi1 and Six2.

[0986] According to any aspect of the invention, the transcription factors may comprise or consist of Gfi1 , Lhx3 and Six2.

[0987] According to any aspect of the invention, the transcription factors may comprise or consist of Pou4f3, Gfi1 and Lhx3.

[0988] According to any aspect of the invention, the transcription factors may comprise or consist of Pou4f3, Gfi1 and Six2.

[0989] According to any aspect of the invention, the transcription factors may comprise or consist of Pou4f3, Gfi1 , Lhx3 and Six2. As used herein, “Six'! ” refers to refers to SIX homeobox 1 . In humans it is encoded by the SIX1 gene, also known as Sine Oculis Homeobox Homolog 1 , Homeobox Protein SIX1 , DFNA23, TIP39 and BOS3. In humans, the Ensembl gene ID is ENSG00000126778, such as ENSG00000126778.12. An example of a transcript is the Ensembl transcript ID ENST00000645694, such as ENST00000645694.3 and the UniProt ID is Q15475, such as Q15475 v1 ; codon-optimised and alternatively spliced transcript variants are encompassed.

[0990] SIX1 may refer to the human sequence having the following amino acid sequence, identified as SEQ ID NO: 54.

[0991] SEQ ID NO: 54

[0992] MSMLPSFGFTQEQVACVCEVLQQGGNLERLGRFLWSLPACDHLHKNESVLKAKAVVAFHRGNFRELYKI LESHQFSPHNHPKLQQLWLKAHYVEAEKLRGRPLGAVGKYRVRRKFPLPRTIWDGEETSYCFKEKSRGV LREWYAHNPYPSPREKRELAEATGLTTTQVSNWFKNRRQRDRAAEAKERENTENNNSSSNKQNQLSPL EGGKPLMSSSEEEFSPPQSPDQNSVLLLQGNMGHARSSNYSLPGLTASQPSHGLQTHQHQLQDSLLGP LTSSLVDLGS

[0993] SIX1 may be encoded by the following human coding sequence, identified as SEQ ID NO: 55

[0994] SEQ ID NO: 55

[0995] ATGTCGATGCTGCCGTCGTTTGGCTTTACGCAGGAGCAAGTGGCGTGCGTGTGCGAGGTTCTGCAG CAAGGCGGAAACCTGGAGCGCCTGGGCAGGTTCCTGTGGTCACTGCCCGCCTGCGACCACCTGCA CAAGAACGAGAGCGTACTCAAGGCCAAGGCGGTGGTCGCCTTCCACCGCGGCAACTTCCGTGAGCT CTACAAGATCCTGGAGAGCCACCAGTTCTCGCCTCACAACCACCCCAAACTGCAGCAACTGTGGCTG AAGGCGCATTACGTGGAGGCCGAGAAGCTGCGCGGCCGACCCCTGGGCGCCGTGGGCAAATATCG GGTGCGCCGAAAATTTCCACTGCCGCGCACCATCTGGGACGGCGAGGAGACCAGCTACTGCTTCAA GGAGAAGTCGAGGGGTGTCCTGCGGGAGTGGTACGCGCACAATCCCTACCCATCGCCGCGTGAGA AGCGGGAGCTGGCCGAGGCCACCGGCCTCACCACCACCCAGGTCAGCAACTGGTTTAAGAACCGG AGGCAAAGAGACCGGGCCGCGGAGGCCAAGGAAAGGGAGAACACCGAAAACAATAACTCCTCCTC CAACAAGCAGAACCAACTCTCTCCTCTGGAAGGGGGCAAGCCGCTCATGTCCAGCTCAGAAGAGGA ATTCTCACCTCCCCAAAGTCCAGACCAGAACTCGGTCCTTCTGCTGCAGGGCAATATGGGCCACGCC AGGAGCTCAAACTATTCTCTCCCGGGCTTAACAGCCTCGCAGCCCAGTCACGGCCTGCAGACCCAC CAGCATCAGCTCCAAGACTCTCTGCTCGGCCCCCTCACCTCCAGTCTGGTGGACTTGGGGTCC

[0996] The nucleic acid sequence may encode SIX1 or functional variant thereof. The nucleotide sequence encoding SIX1 may comprise SEQ ID NO: 55. The term ’functional variant(s)’ has been defined in the application in relation to transcription factors such as Pou4f3, Gfi1 , Lhx3 and Six2. This definition applies analogously to Six1 . By way of non-limiting example, a nucleotide sequence may have at least 60% identity to SEQ ID NO: 55, such as at least 70%, 75%, 80%, 85%, 90% or 95% identity to SEQ ID NO: 55. By way of further non-limiting example, a functional variant of SIX1 may comprise an amino acid sequence at least 70% identical to SEQ ID NO: 54. The transcription factors according to the present invention may be defined as not comprising Six1 . The transcription factors may be defined as not comprising Six1 or a functional variant thereof.

[0997] The nucleic acid molecule, system, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any aspect of the invention may be defined as not comprising, encoding, targeting, introducing or increasing the expression of Six1 , as applicable. The nucleic acid molecule, system, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any aspect of the invention may be defined as not comprising, encoding, targeting, introducing or increasing the expression of Six1 or a functional variant thereof, as applicable.

[0998] In alternative statements of the invention described elsewhere herein, Six1 or a functional variant thereof may be defined in accordance with any one or more of the statements concerning Six1 herein.

[0999] Each of the transcription factor combinations represented above were delivered to experimental systems as detailed in the Examples. Without being bound by theory, they may be associated with surprising technical effects, for example as further described below.

[1000] The at least two transcription factors may comprise Pou4f3 and Gfi1. While Pou4f3 and Gfi1 have been used together as part of the GPA combination, it is thought they have not previously been used together for cochlear cell reprogramming in the absence of Atohl . The inventors believe the failure to investigate cochlear cell reprogramming by Pou4f3 and Gfi1 without Atohl is best explained by the technical prejudice in the art to supplementing, rather than replacing Atohl . The data disclosed herein allows comparison of the effects of Pou4f3 and Gfi 1 with both Atohl alone and with GPA. Immunohistochemical data surprisingly indicate that Pou4f3 and Gfi1 , without Atohl , is an alternative to GPA for generating Myo7a positive cells (thought to include both immature and mature cochlear hair cells). Immunohistochemical data also surprisingly indicate that Pou4f3 and Gfi1 , without Atohl , generates more Myo7a positive cells than Atohl alone. Furthermore, Pou4f3 and Gfi1 were also supplemented by additional transcription factors (without Atohl) in further combinations described herein. Combinations comprising Pou4f3 and Gfi1 , but not Atohl , are surprisingly shown herein to upregulate the mature hair cell marker Prestin (not seen using Atohl alone or GPA), while avoiding the generation of “P1-like” immature hair cells seen with Atohl alone or GPA. Combinations comprising Pou4f3 and Gfi1 , but not Atohl , may therefore surprisingly improve the maturity of reprogrammed cochlear hair cells compared to known combinations based on Atohl . Furthermore, expression of Atohl in adult mice in vivo is shown herein to lead to a partial loss of inner hair cells, an effect which is exacerbated by the addition of Pou4f3 and Gfi1 alongside Atohl . Surprisingly, three transcription factor combinations that include Pou4f3 and Gfi1 but not Atohl are shown to significantly reduce the inner hair cell loss caused by GPA expression in adult mice in vivo. Without being bound by theory, the advantageous reduction in inner hair cell loss relative to GPA may be driven, at least in part, but the use of Pou4f3 and Gfi1 but not Atohl , in these combinations. Combinations comprising Pou4f3 and Gfi1 , but not Atohl , may therefore surprisingly reduce toxicity to cochlear inner hair cells compared to known combinations based on Atohl . Taken together, such combinations may therefore solve the problem of providing an improved therapeutic for transcription factor based cochlear reprogramming. Without being bound by theory, further advantages may arise from adding additional transcription factors to Pou4f3 and Gfi1.

[1001] Therefore, the nucleic acid molecule of the first aspect may comprise Pou4f3 and Gfi1 , or functional variants thereof. The nucleic acid molecule of the first aspect may consist Pou4f3 and Gfi1 , or functional variants thereof.

[1002] The at least two transcription factors may comprise Gfi1 and Lhx3. It is thought that Gfi1 and Lhx3 have not previously been used together for cochlear cell reprogramming, let alone used together in the absence of Atohl . The data presented herein demonstrates that there is synergy between Gfi1 and Lhx3 (i.e. the combination of Gfi1 and Lhx3 drives a significantly greater increase in a cochlear hair cell gene signature compared with what would be expected for the additive effect of Gfi1 and Lhx3). In addition, the data presented herein enable a comparison of the effects of Gfi1 and Lhx3 with GPA on the upregulation of cochlear hair cell signature genes following combined transcription factor treatment in human cells. Surprisingly, Gfi 1 and Lhx3 were shown to have more synergy in activating these signature genes than GP does when combined with A. This suggests that such combinations could offer an improved therapeutic approach for transcription factor-based cochlear reprogramming.

[1003] Therefore, the nucleic acid molecule of the first aspect may comprise Gfi1 and Lhx3, or functional variants thereof. The nucleic acid molecule of the first aspect may comprise Gfi1 and Lhx3, or functional variants thereof and may not comprise Atohl or functional variants thereof.

[1004] Therefore, the nucleic acid molecule of the first aspect may consist Gfi1 and Lhx3, or functional variants thereof. The nucleic acid molecule of the first aspect may consist Gfi1 and Lhx3, or functional variants thereof and may not comprise Atohl or functional variants thereof.

[1005] According to an alternative statement of the first aspect, wherein the nucleic acid molecule encodes Gfi1 and Lhx3, the nucleic acid molecule may further encode Atohl or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Gfi1 , Lhx3, and Atohl , or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Gfi1 , Lhx3 and Atohl .

[1006] The at least two transcription factors may comprise Gfi1 and Six2. It is thought that Gfi 1 and Six2 have not previously been used together for cochlear cell reprogramming, let alone used together in the absence of Atohl . The data presented herein demonstrates that there is synergy between Gfi1 and Six2 (i.e. the combination of Gfi1 and Six2 drives a significantly greater increase in a cochlear hair cell gene signature compared with what would be expected for the additive effect of Gfi1 and Six2). In addition, the data presented herein enable a comparison of the effects of Gfi1 and Six2 with GPA on the upregulation of cochlear hair cell signature genes following combined transcription factor treatment in human cells. Surprisingly, Gfi1 and Six2 were shown to have more synergy in activating these signature genes than GP does when combined with A. This suggests that such combinations could offer an improved therapeutic approach for transcription factor-based cochlear reprogramming. Therefore, the nucleic acid molecule of the first aspect may comprise Gfi1 and Six2, or functional variants thereof. The nucleic acid molecule of the first aspect may comprise Gfi1 and Six2, or functional variants thereof and may not comprise Atohl or functional variants thereof.

[1007] Therefore, the nucleic acid molecule of the first aspect may consist Gfi1 and Six2, or functional variants thereof. The nucleic acid molecule of the first aspect may consist Gfi1 and Six2, or functional variants thereof and may not comprise Atohl or functional variants thereof.

[1008] According to an alternative statement of the first aspect, wherein the nucleic acid molecule encodes Gfi1 and Six2, the nucleic acid molecule may further encode Atohl or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Gfi1 , Six2, and Atohl , or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Gfi1 , Six2 and Atohl .

[1009] According to any aspect of the inventions, the transcription factors may comprise Pou4f3, Gfi1 and at least one further transcription factor. The at least one further transcription factor may be selected from the group consisting of Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3. The transcription factors may comprise Pou4f3, Gfi 1 and at least two further transcription factors. The at least two further transcription factors may each be selected from the group consisting of Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. Imputation of expression values based on downstream network activation suggests that expression levels of Kcnip3 and / or Pknox2 may be sub- optimal in the combinations as specifically exemplified in the Examples. The at least one further transcription factor may therefore be selected from the group consisting of Lhx3, Isl1 , Six2 and Pknox2. The at least one further transcription factor may therefore be selected from the group consisting of Lhx3, Isl1 , Six2 and Kcnip3. The at least one further transcription factor may be selected from the group consisting of Lhx3, Isl1 and Six2. Therefore, according to any aspect of the invention, the transcription factors may comprise:

[1010] (a) Pou4f3, Gfi1 , Lhx3 and Six2;

[1011] (b) Pou4f3, Gfi1 and Lhx3;

[1012] (c) Pou4f3, Gfi1 and Six2;

[1013] (d) Pou4f3, Gfi1 and Isl1 ;

[1014] (e) Pou4f3, Gfi1 and Pknox2;

[1015] (f) Pou4f3, Gfi1 and Kcnip3; or

[1016] (g) Pou4f3 and Gfi1 .

[1017] Therefore, according to any aspect of the invention, the transcription factors may consist:

[1018] (a) Pou4f3, Gfi1 , Lhx3 and Six2;

[1019] (b) Pou4f3, Gfi1 and Lhx3;

[1020] (c) Pou4f3, Gfi1 and Six2;

[1021] (d) Pou4f3, Gfi1 and Isl1 ;

[1022] (e) Pou4f3, Gfi1 and Pknox2;

[1023] (f) Pou4f3, Gfi1 and Kcnip3; or (g) Pou4f3 and Gfi1 .

[1024] According to any aspect of the inventions, the transcription factors may comprise Gfi1 , Lhx3 and at least one further transcription factor. The at least one further transcription factor may be selected from the group consisting of Pou4f3, Six2, Isl1 Pknox2 and Kcnip3. The transcription factors may comprise Gfi1 , Lhx3 and at least two further transcription factors. The at least two further transcription factors may each be selected from the group consisting of Pou4f3, Six2, Isl1 , Pknox2 and Kcnip3. Imputation of expression values based on downstream network activation suggests that expression levels of Kcnip3 and / or Pknox2 may be sub- optimal in the combinations as specifically exemplified in the Examples. The at least one further transcription factor may therefore be selected from the group consisting of Pou4f3, Six2, Isl1 and Pknox2. The at least one further transcription factor may therefore be selected from the group consisting of Pou4f3, Six2, Isl1 and Kcnip3. The at least one further transcription factor may be selected from the group consisting of Pou4f3, Six2, and Isl1 . Therefore, according to any aspect of the invention, the transcription factors may comprise:

[1025] (a) Gfi1 and Lhx3;

[1026] (b) Gfi1 , Lhx3 and Pou4f3;

[1027] (c) Gfi 1 , Lhx3 and Six2;

[1028] (d) Gfi1 , Lhx3, Pou4f3 and Six2

[1029] (e) Gfi1 , Lhx3 and Isl1 ;

[1030] (f) Gfi 1 , Lhx3 and Pknox2; or

[1031] (g) Gfi1 , Lhx3 and Kcnip3.

[1032] Therefore, according to any aspect of the invention, the transcription factors may consist:

[1033] (a) Gfi1 and Lhx3;

[1034] (b) Gfi1 , Lhx3 and Pou4f3;

[1035] (c) Gfi 1 , Lhx3 and Six2;

[1036] (d) Gfi1 , Lhx3, Pou4f3 and Six2

[1037] (e) Gfi1 , Lhx3 and Isl1 ;

[1038] (f) Gfi 1 , Lhx3 and Pknox2; or

[1039] (g) Gfi1 , Lhx3 and Kcnip3.

[1040] According to any aspect of the inventions, the transcription factors may comprise Gfi1 , Six2 and at least one further transcription factor. The at least one further transcription factor may be selected from the group consisting of Pou4f3, Lhx3, Isl 1 Pknox2 and Kcnip3. The transcription factors may comprise Gfi 1 , Six2 and at least two further transcription factors. The at least two further transcription factors may each be selected from the group consisting of Pou4f3, Lhx3, Isl 1 , Pknox2 and Kcnip3. Imputation of expression values based on downstream network activation suggests that expression levels of Kcnip3 and / or Pknox2 may be sub- optimal in the combinations as specifically exemplified in the Examples. The at least one further transcription factor may therefore be selected from the group consisting of Pou4f3, Lhx3, Isl 1 and Pknox2. The at least one further transcription factor may therefore be selected from the group consisting of Pou4f3, Lhx3, Isl1 and Kcnip3. The at least one further transcription factor may be selected from the group consisting of Pou4f3, Lhx3, and Isl 1 . Therefore, according to any aspect of the invention, the transcription factors may comprise:

[1041] (a) Gfi1 and Six2;

[1042] (b) Gfi1 , Six2 and Pou4f3;

[1043] (c) Gfi 1 , Six2 and Lhx3;

[1044] (d) Gfi1 , Six2, Pou4f3 and Lhx3;

[1045] (e) Gfi1 , Six2, and Isl1 ;

[1046] (f) Gfi 1 , Six2, and Pknox2; or

[1047] (g) Gfi1 , Six2, and Kcnip3.

[1048] Therefore, according to any aspect of the invention, the transcription factors may consist:

[1049] (a) Gfi1 and Six2;

[1050] (b) Gfi1 , Six2 and Pou4f3;

[1051] (c) Gfi 1 , Six2 and Lhx3;

[1052] (d) Gfi1 , Six2, Pou4f3 and Lhx3;

[1053] (e) Gfi1 , Six2, and Isl1 ;

[1054] (f) Gfi 1 , Six2, and Pknox2; or

[1055] (g) Gfi1 , Six2, and Kcnip3.

[1056] The at least two transcription factors may comprise Lhx3 and Six2. It is thought that Lhx3 and Six2 have not previously been used together for cochlear cell reprogramming, let alone used together in the absence of Atohl . A combination comprising Lhx3 and Six2, but notAtohl , is surprisingly shown herein to upregulate the mature hair cell marker Prestin (not seen using Atohl alone or GPA), while avoiding the generation of “P1-like” immature hair cells seen with Atohl alone or GPA. Combinations comprising Lhx3 and Six2 may therefore surprisingly improve the maturity of reprogrammed cochlear hair cells compared to known combinations based on Atohl . Furthermore, a combination comprising Lhx3 and Six2, but not Atohl , is surprisingly shown herein to significantly reduce the inner hair cell loss caused by GPA expression. Combinations comprising Lhx3 and Six2 may therefore surprisingly reduce toxicity to cochlear inner hair cells compared to known combinations based on Atohl . Taken together, such combinations may therefore solve the problem of providing an improved therapeutic for transcription factor based cochlear reprogramming.

[1057] Therefore, the nucleic acid molecule of the first aspect may comprise Lhx3 and Six2, or functional variants thereof. The nucleic acid molecule of the first aspect may consist Lhx3 and Six2, or functional variants thereof.

[1058] According to an alternative statement of the first aspect, wherein the nucleic acid molecule encodes Lhx3 and Six2, the nucleic acid molecule may further encode Atohl or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Lhx3, Six2 and Atohl , or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Lhx3, Six2 and Atohl . The at least two transcription factors may comprise Isl 1 and Kcnip3. It is thought that Isl 1 and Kcnip3 have not previously been used together for cochlear cell reprogramming, let alone used together in the absence of Atohl . A combination comprising Isl1 and Kcnip3, but not Atohl , is surprisingly shown herein to upregulate the mature hair cell marker Prestin (not seen using Atohl alone or GPA), while avoiding the generation of “P1-like” immature hair cells seen with Atohl alone or GPA. Combinations comprising Isl1 and Kcnip3 may therefore surprisingly improve the maturity of reprogrammed cochlear hair cells compared to known combinations based on Atohl . Furthermore, a combination comprising Isl1 and Kcnip3, but not Atohl , is surprisingly shown herein to significantly reduce the inner hair cell loss caused by GPA express ion. Combinations comprising Isl1 and Kcnip3 may therefore surprisingly reduce toxicity to cochlear inner hair cells compared to known combinations based on Atohl . Taken together, such combinations may therefore solve the problem of providing an improved therapeutic for transcription factor based cochlear reprogramming.

[1059] Therefore, the nucleic acid molecule of the first aspect may comprise Isl1 and Kcnip3, or functional variants thereof. The nucleic acid molecule of the first aspect may consist Isl1 and Kcnip3, or functional variants thereof.

[1060] According to an alternative statement of the first aspect, wherein the nucleic acid molecule encodes Isl1 and Kcnip3, the nucleic acid molecule may further encode Atohl , or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Isl1 , Kcnip3 and Atohl , or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Isl1 , Kcnip3 and Atohl .

[1061] The at least two transcription factors may comprise Pknox2 and Kcnip3. It is thought that Pknox2 and Kcnip3 have not previously been used together for cochlear cell reprogramming, let alone used together in the absence of Atohl . A combination comprising Pknox2 and Kcnip3, but not Atohl , is surprisingly shown herein to upregulate the mature hair cell marker Prestin (not seen using Atohl alone or GPA), while avoiding the generation of “P1-like” immature hair cells seen with Atohl alone or GPA. Combinations comprising Pknox2 and Kcnip3 may therefore surprisingly improve the maturity of reprogrammed cochlear hair cells compared to known combinations based on Atohl . Furthermore, a combination comprising Pknox2 and Kcnip3, but not Atohl , is surprisingly shown herein to significantly reduce the inner hair cell loss caused by GPA expression. Combinations comprising Pknox2 and Kcnip3 may therefore surprisingly reduce toxicity to cochlear inner hair cells compared to known combinations based on Atohl . Taken together, such combinations may therefore solve the problem of providing an improved therapeutic for transcription factor based cochlear reprogramming.

[1062] Therefore, the nucleic acid molecule of the first aspect may comprise Pknox2 and Kcnip3, or functional variants thereof. The nucleic acid molecule of the first aspect may consist Pknox2 and Kcnip3, or functional variants thereof.

[1063] According to an alternative statement of the first aspect, wherein the nucleic acid molecule encodes Pknox2 and Kcnip3, the nucleic acid molecule may further encode Atohl , or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pknox2, Kcnip3 and Atohl , or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pknox2, Kcnip3 and Atohl .

[1064] The at least two transcription factors may comprise Pou4f3, Gfi 1 and Kcnip3. It is thought that Pou4f3, Gfi1 and Kcnip3 have not previously been used together for cochlear cell reprogramming, let alone used together in the absence of Atohl . More than one combination comprising Pou4f3, Gfi1 and Kcnip3, but not Atohl , is surprisingly shown herein to upregulate the mature hair cell marker Prestin (not seen using Atohl alone or GPA), while avoiding the generation of “P1 -like” immature hair cells seen with Atohl alone or GPA. Combinations comprising Pou4f3, Gfi1 and Kcnip3 may therefore surprisingly improve the maturity of reprogrammed cochlear hair cells compared to known combinations based on Atohl . Furthermore, more than one combination comprising Pou4f3, Gfi1 and Kcnip3, but not Atohl , is surprisingly shown herein to significantly reduce the inner hair cell loss caused by GPA expression. Combinations comprising Pou4f3, Gfi1 and Kcnip3 may therefore surprisingly reduce toxicity to cochlear inner hair cells compared to known combinations based on Atohl . Taken together, such combinations may therefore solve the problem of providing an improved therapeutic for transcription factor based cochlear reprogramming.

[1065] Therefore, the nucleic acid molecule ofthe first aspect may comprise Pou4f3, Gfi1 and Kcnip3, or functional variants thereof. The nucleic acid molecule of the first aspect may consist Pou4f3, Gfi1 and Kcnip3, or functional variants thereof.

[1066] According to an alternative statement ofthe first aspect, wherein the nucleic acid molecule encodes Pou4f3, Gfi1 and Kcnip3, the nucleic acid molecule may further encode Atohl , or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi1 , Kcnip3 and Atohl , or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi 1 , Kcnip3 and Atohl .

[1067] The at least two transcription factors may comprise Pou4f3, Gfi1 and Lhx3. It is thought that Pou4f3, Gfi1 and Lhx3 have not previously been used together for cochlear cell reprogramming, let alone used together in the absence of Atohl . The data presented herein demonstrates that there is synergy between Pou4f3, Gfi1 and Lhx3 (i.e. the combination of Gfi1+Six2 with Lhx3, or the combination of Gfi1+Lhx3 with Pou4f3 drives a significantly greater increase in a cochlear hair cell gene signature compared with what would be expected for the additive effect of Lhx3 with Gfi1 + Six2 or Pou4f3 with Gfi1+Lhx3 respectively). In addition, the data presented herein enable a comparison of the effects of Pou4f3, Gfi1 and Lhx3 with GPA on the upregulation of cochlear hair cell signature genes following combined transcription factor treatment in human cells. Surprisingly, Pou4f3, Gfi1 and Lhx3 were shown to upregulate these genes more effectively than GPA. This suggests that such combinations could offer an improved therapeutic approach for transcription factor-based cochlear reprogramming.

[1068] More than one combination comprising Pou4f3, Gfi1 and Lhx3, but not Atohl , is surprisingly shown herein to upregulate the mature hair cell marker Prestin (not seen using Atohl alone or GPA), while avoiding the generation of “P1 -like” immature hair cells seen with Atohl alone or GPA. Combinations comprising Pou4f3, Gfi1 and Lhx3 may therefore surprisingly improve the maturity of reprogrammed cochlear hair cells compared to known combinations based on Atohl . Furthermore, more than one combination comprising Pou4f3, Gfi1 and Lhx3, but not Atohl , is surprisingly shown herein to significantly reduce the inner hair cell loss caused by GPA expression. Combinations comprising Pou4f3, Gfi1 and Lhx3 may therefore surprisingly reduce toxicity to cochlear inner hair cells compared to known combinations based on Atohl . Taken together, such combinations may therefore solve the problem of providing an improved therapeutic for transcription factor based cochlear reprogramming.

[1069] Therefore, the nucleic acid molecule of the first aspect may comprise Pou4f3, Gfi1 and Lhx3, or functional variants thereof. The nucleic acid molecule of the first aspect may comprise Pou4f3, Gfi1 and Lhx3, or functional variants thereof and may not comprise Atohl or functional variants thereof.

[1070] Therefore, the nucleic acid molecule of the first aspect may consist Pou4f3, Gfi1 and Lhx3, or functional variants thereof. The nucleic acid molecule of the first aspect may consist Pou4f3, Gfi1 and Lhx3, or functional variants thereof and may not comprise Atohl or functional variants thereof.

[1071] According to an alternative statement of the first aspect, wherein the nucleic acid molecule encodes Pou4f3, Gfi1 and Lhx3, the nucleic acid molecule may further encode Atohl , or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi1 , Lhx3 and Atohl , or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi1 , Lhx3 and Atohl .

[1072] The at least two transcription factors may comprise Pou4f3, Gfi1 and Six2. It is thought that Pou4f3, Gfi1 and Six2 have not previously been used together for cochlear cell reprogramming, let alone used together in the absence of Atohl . The data presented herein demonstrates that there is synergy between Pou4f3, Gfi1 and Six2 (i.e. the combination of Gfi1 +Six2 with Pou4f3, or the combination of Gfi1 +Pou4f3 with Six2 drives a significantly greater increase in a cochlear hair cell gene signature compared with what would be expected for the additive effect of Pou4f3 with Gfi1 + Six2 or Six2 with Gfi1 + Pou4f3 respectively). In addition, the data presented herein enable a comparison of the effects of Pou4f3, Gfi1 and Six2 with GPA on the upregulation of cochlear hair cell signature genes following combined transcription factor treatment in human cells. Surprisingly, Pou4f3, Gfi 1 and Six2 were shown to upregulate these genes more effectively than GPA. This suggests that such combinations could offer an improved therapeutic approach for transcription factor-based cochlear reprogramming.

[1073] Therefore, the nucleic acid molecule of the first aspect may comprise Pou4f3, Gfi1 and Six2, or functional variants thereof. The nucleic acid molecule of the first aspect may comprise Pou4f3, Gfi1 and Six2, or functional variants thereof and may not comprise Atohl or functional variants thereof.

[1074] Therefore, the nucleic acid molecule of the first aspect may consist Pou4f3, Gfi1 and Six2, or functional variants thereof. The nucleic acid molecule of the first aspect may consist Pou4f3, Gfi1 and Six2, or functional variants thereof and may not comprise Atohl or functional variants thereof. According to an alternative statement of the first aspect, wherein the nucleic acid molecule encodes Pou4f3, Gfi1 and Six2, the nucleic acid molecule may further encode Atohl , or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi1 , Six2 and Atohl , or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi1 , Six2 and Atohl .

[1075] The at least two transcription factors may comprise Pou4f3, Gfi 1 , Lhx3 and Six2. The data disclosed herein allows comparison of the effects of Pou4f3, Gfi1 , Lhx3 and Six2 with both Atohl alone and with GPA. Immunohistochemical data surprisingly indicate that Pou4f3, Gfi1 , Lhx3 and Six2, without Atohl , is an alternative to GPA for generating Myo7a positive cells (thought to include both immature and mature cochlear hair cells). Immunohistochemical data also surprisingly indicate that Pou4f3, Gfi1 , Lhx3 and Six2, without Atohl , generates more Myo7a positive cells than Atohl alone. The combination of Pou4f3, Gfi1 , Lhx3 and Six2, is surprisingly shown herein to upregulate the mature hair cell marker Prestin (not seen using Atohl alone or GPA), while avoiding the generation of “P1-like” immature hair cells seen with Atohl alone or GPA. Analysis of snRNAseq data using force-directed layout / RNA velocity shows a small Myo7a+ Sox2+ population with direct movement towards mature hair cells, which is not seen in Atohl alone or GPA samples. Some induced hair cells produced by Pou4f3, Gfi1 , Lhx3 and Six2 are more similar to OHC / IHC than to “P1-like” immature hair cells induced by Atohl alone or GPA. This is seen from force-directed layout plots, showing some Pou4f3, Gfi1 , Lhx3 and Six2-induced hair cells are located close to OHCs, whereas most GPA and Atohl alone induced “P1 -like” hair cells form distinct clusters more distant from IHCs / OHCs. Together, these data suggest that Pou4f3, Gfi1 , Lhx3 and Six2 may bypass the generation of “P1-like” immature hair cells, instead setting support cells on a conversion trajectory moving more directly towards mature hair cells. Combinations comprising Pou4f3, Gfi 1 , Lhx3 and Six2 may therefore surprisingly improve the maturity of reprogrammed cochlear hair cells compared to known combinations based on Atohl . Furthermore, a combination comprising Pou4f3, Gfi1 , Lhx3 and Six2, is surprisingly shown herein to significantly reduce the inner hair cell loss caused by GPA expression. Combinations comprising Pou4f3, Gfi1 , Lhx3 and Six2 may therefore surprisingly reduce toxicity to cochlear inner hair cells compared to known combinations based on Atohl . Taken together, such combinations may therefore solve the problem of providing an improved therapeutic for transcription factor based cochlear reprogramming.

[1076] Therefore, the nucleic acid molecule of the first aspect may comprise Pou4f3, Gfi1 , Lhx3 and Six2, or functional variants thereof. The nucleic acid molecule of the first aspect may consist Pou4f3, Gfi1 , Lhx3 and Six2, or functional variants thereof.

[1077] According to an alternative statement of the first aspect, wherein the nucleic acid molecule encodes Pou4f3, Gfi1 , Lhx3 and Six2, the nucleic acid molecule may further encode Atohl , or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi1 , Lhx3, Six2 and Atohl , or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi1 , Lhx3, Six2 and Atohl .

[1078] The at least two transcription factors may comprise Pou4f3, Gfi1 , Isl1 and Kcnip3. Immunohistochemical data disclosed herein surprisingly indicate that Pou4f3, Gfi1 , Isl1 and Kcnip3, without Atohl , generates more Myo7a positive cells than Atohl alone. The combination of Pou4f3, Gfi1 , Isl1 and Kcnip3, is surprisingly shown herein to upregulate the mature hair cell marker Prestin (not seen using Atohl alone or GPA), while avoiding the generation of “P1 -like” immature hair cells seen with Atohl alone or GPA. Analysis of snRNAseq data using force-directed layout / RNA velocity shows a small Myo7a+ Sox2+ population with direct movement towards mature hair cells, which is not seen in Atohl alone or GPA samples. Some induced hair cells produced by Pou4f3, Gfi 1 , Isl 1 and Kcnip3 are more similar to OHC / IHC than to “P 1 -like” immature hair cells induced by Atohl alone or GPA. This is seen from force-directed layout plots, showing some Pou4f3, Gfi1 , Isl 1 and Kcnip3-induced hair cells are located close to OHCs, whereas most GPA and Atohl alone induced “P1 -like” hair cells form distinct clusters more distant from IHCs / OHCs. Together, these data suggest that Pou4f3, Gfi 1 , Isl 1 and Kcnip3 may bypass the generation of “P 1 -like” immature hair cells, instead setting support cells on a conversion trajectory moving more directly towards mature hair cells. Combinations comprising Pou4f3, Gfi1 , Isl1 and Kcnip3 may therefore surprisingly improve the maturity of reprogrammed cochlear hair cells compared to known combinations based on Atohl . Furthermore, a combination comprising Pou4f3, Gfi1 , Isl1 and Kcnip3, is surprisingly shown herein to significantly reduce the inner hair cell loss caused by GPA expression. Combinations comprising Pou4f3, Gfi1 , Isl1 and Kcnip3 may therefore surprisingly reduce toxicity to cochlear inner hair cells compared to known combinations based on Atohl . Taken together, such combinations may therefore solve the problem of providing an improved therapeutic for transcription factor based cochlear reprogramming.

[1079] Therefore, the nucleic acid molecule of the first aspect may comprise Pou4f3, Gfi1 , Isl1 and Kcnip3, or functional variants thereof. The nucleic acid molecule of the first aspect may consist Pou4f3, Gfi1 , Isl1 and Kcnip3, or functional variants thereof.

[1080] According to an alternative statement of the first aspect, wherein the nucleic acid molecule encodes Pou4f3, Gfi1 , Isl1 and Kcnip3, the nucleic acid molecule may further encode Atohl , or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi1 , Isl1 , Kcnip3 and Atohl , or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi1 , Isl1 , Kcnip3 and Atohl .

[1081] The at least two transcription factors may comprise Pou4f3, Gfi1 , Pknox2 and Kcnip3. The data disclosed herein allows comparison of the effects of Pou4f3, Gfi 1 , Pknox2 and Kcnip3 with both Atohl alone and with GPA. Immunohistochemical data surprisingly indicate that Pou4f3, Gfi1 , Pknox2 and Kcnip3, without Atohl , is an alternative to GPA for generating Myo7a positive cells (thought to include both immature and mature cochlear hair cells). Immunohistochemical data also surprisingly indicate that Pou4f3, Gfi1 , Pknox2 and Kcnip3, without Atohl , generates more Myo7a positive cells than Atohl alone. The combination Pou4f3, Gfi1 , Pknox2 and Kcnip3, is surprisingly shown herein to upregulate the mature hair cell marker Prestin (not seen using Atohl alone or GPA), while avoiding the generation of “P1 -like” immature hair cells seen with Atohl alone or GPA. Analysis of snRNAseq data using force-directed layout I RNA velocity shows a small Myo7a+ Sox2+ population with direct movement towards mature hair cells, with a possible cell differentiation trajectory between supporting cells and hair cells, which is not seen in Atohl alone or GPA samples. Some induced hair cells produced by Pou4f3, Gfi1 , Pknox2 and Kcnip3 are more similar to OHC / IHC than to “P1 -like” immature hair cells induced by Atohl alone or GPA. This is seen from force- directed layout plots, showing some Pou4f3, Gfi1 , Pknox2 and Kcnip3-induced hair cells are located close to OHCs, whereas most GPA and Atohl alone induced “P1-like” hair cells form distinct clusters more distant from IHCs / OHCs. Together, these data suggest that Pou4f3, Gfi1 , Pknox2 and Kcnip3 may bypass the generation of “P1 -like” immature hair cells, instead setting support cells on a conversion trajectory moving more directly towards mature hair cells. Combinations comprising Pou4f3, Gfi1 , Pknox2 and Kcnip3 may therefore surprisingly improve the maturity of reprogrammed cochlear hair cells compared to known combinations based on Atohl . Furthermore, a combination comprising Pou4f3, Gfi1 , Pknox2 and Kcnip3, is surprisingly shown herein to significantly reduce the inner hair cell loss caused by GPA expression. Combinations comprising Pou4f3, Gfi1 , Pknox2 and Kcnip3 may therefore surprisingly reduce toxicity to cochlear inner hair cells compared to known combinations based on Atohl . Taken together, such combinations may therefore solve the problem of providing an improved therapeutic fortranscription factor based cochlear reprogramming.

[1082] Therefore, the nucleic acid molecule of the first aspect may comprise Pou4f3, Gfi1 , Pknox2 and Kcnip3, or functional variants thereof. The nucleic acid molecule of the first aspect may consist Pou4f3, Gfi1 , Pknox2 and Kcnip3, or functional variants thereof.

[1083] According to an alternative statement of the first aspect, wherein the nucleic acid molecule encodes Pou4f3, Gfi1 , Pknox2 and Kcnip3, the nucleic acid molecule may further encode Atohl , or a functional variant thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi1 , Pknox2, Kcnip3 and Atohl , or a functional variant of any thereof. Any aspect of the invention may therefore be described in the alternative as relating to Pou4f3, Gfi1 , Pknox2, Kcnip3 and Atohl . “Sequence identity” refers to the similarity between amino acid (or nucleotide) sequences. Sequence identity is frequently measured in terms of percentage identity (or similarity or homology); the higher the percentage, the more similar the two sequences are. While there exist a number of methods to measure identity between two polypeptide or two polynucleotide sequences, methods commonly employed to determine identity are codified in computer programs. Preferred computer programs to determine identity between two sequences include, but are not limited to, GCG program package (Devereux, et ai, Nucleic acids Research, 12, 387 (1984), BLASTP, BLASTN, and FASTA (Atschul et ai, J. Molec. Biol. (1990) 215, 403). Preferably, a sequence has at least 70% identity, using the default parameters ofthe BLAST computer program (Atschul et al., J. Mol. Biol. (1990) 215, 403-410) provided by HGMP (Human Genome Mapping Project), to a sequence disclosed herein.

[1084] The term a “variant” in referring to protein and nucleic acid sequences (including the Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2, Kcnip3 and Atohl sequences provided herein) are typically characterised by possession of at least 60%, 70%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% sequence identity counted over the full length alignment with the amino acid or nucleotide sequences. The present invention contemplates the use of variants of the nucleic acid sequences, promoters and transcription factors described herein. The variant could be a fragment of a full-length sequence, a codon-optimised sequence, or a naturally occurring splice variant. The variant could be a polypeptide or nucleic acid molecule at least 60%, 70%, 80%, 85%, 90%, 95%, 98%, or 99% identical to a full length sequence, wherein the fragment is at least 50%, 60%, 70%, 80%, 85%, 90%, 95%, 98%, or 99% as long as the full length wild type polypeptide or nucleic acid molecule, or a domain thereof has a functional activity of interest such as the ability to promote conversion of a source cell type to a target cell type. The domain may be at least 100, 200, 300, or 400 amino acids in length, beginning at any amino acid position in the sequence and extending toward the C-terminus. Variations known in the art to eliminate or substantially reduce the activity of the protein may be avoided. The variant may lack an N- and / or C-terminal portion of the full-length polypeptide, e.g., up to 10, 20, or 50 amino acids from either terminus is lacking. The polypeptide may have the sequence of a mature (full length) polypeptide, by which is meant a polypeptide that has had one or more portions such as a signal peptide removed during normal intracellular proteolytic processing (e.g., during co-translational or post- translational processing). When the protein is produced other than by purifying it from cells that naturally express it, the protein may be a chimeric polypeptide, by which is meant that it contains portions from two or more different species. When a protein is produced other than by purifying it from cells that naturally express it, the protein may be a derivative, by which is meant that the protein may comprise additional sequences not related to the protein so long as those sequences do not substantially reduce the biological activity of the protein. One of skill in the art will be aware of, or will readily be able to ascertain, whether a particular polypeptide variant, fragment, or derivative is functional using assays known in the art. Other convenient assays include measuring the ability to activate transcription of a reporter construct containing a transcription factor binding site operably linked to a nucleic acid sequence encoding a detectable marker. For example, the skilled person knows how to perform a luciferase assay to determine whether a variant of a transcription factor is a functional variant. For instance, if the variant activates the luciferase assay and / or has at least 50% of the activity of the full-length wild type polypeptide or nucleic acid molecule, it may be defined as a functional variant. Alternatively, the skilled person may compare transcriptomic changes following exposure to a transcription factor and a variant of the transcription factor, for instance using RNA sequencing, in order to determine whether the variant of the transcription factor is a functional variant. The transcriptomic changes may be upregulation and / or downregulation of gene expression. For instance, if the variant upregulates at least 50% of the genes upregulated by the full-length wild type polypeptide or nucleic acid molecule, it may be defined as a functional variant. Or, if the variant downregulates at least 50% of the genes downregulated by the full-length wild type polypeptide or nucleic acid molecule, it may be defined as a functional variant. Or, if the variant upregulates at least 50% of the genes upregulated by the full-length wild type polypeptide or nucleic acid molecule and downregulates at least 50% of the genes downregulated by the full-length wild type polypeptide or nucleic acid molecule, it may be defined as a functional variant. Alternatively, the skilled person may compare transcriptomic changes in known targets of a transcription factor following exposure to the transcription factor and a variant of the transcription factor, for instance using RT-qPCR, in order to determine whether the variant of the transcription factor is a functional variant. The transcriptomic changes may be upregulation and / or downregulation of the gene expression of the known target. For instance, if the variant upregulates a known target of the transcription factor by at least 50% of the level the known target is upregulated by the full-length wild type polypeptide or nucleic acid molecule, it may be defined as a functional variant. Or, if the variant downregulates a known target of the transcription factor by at least 50% of the level the known target is upregulated by the full-length wild type polypeptide or nucleic acid molecule, it may be defined as a functional variant. Alternatively, the skilled person may compare the effects of a transcription factor and a variant of the transcription factor on cell conversion, for instance by comparing the effects on a reduction in one or more characteristics of a source cell (such as inner ear non-sensory cells) and / or an increase in one or more characteristics of a target cell (such as cochlear hair cells), in order to determine whether the variant of the transcription factor is a functional variant. For instance, if at least 50% of the proportion of cells downregulating one or more source cell characteristic (such as the presence of at least one marker and / or at least one morphological trait of an inner ear non-sensory cell) following exposure to the full-length wild type polypeptide or nucleic acid molecule also downregulate the one or more source cell characteristic following exposure to the variant transcription factor, the variant may be defined as a functional variant. Or, if at least 50% of the proportion of cells upregulating one or more target cell characteristic (such as the presence of at least one marker and / or at least one morphological trait and / or at least one functional characteristic of a cochlear hair cell) following exposure to the full-length wild type polypeptide or nucleic acid molecule also upregulate the one or more target cell characteristic following exposure to the variant transcription factor, the variant may be defined as a functional variant. A functional variant or fragment may have at least 50%, 60%, 70%, 80%, 90%, 95% or more of the activity of the full-length wild type polypeptide or nucleic acid molecule. Afunctional variant or fragment may have at least 50%, 60%, 70%, 80%, 90%, 95% or more of the activity of a codon optimised molecule disclosed herein; references to the full-length wild type polypeptide or nucleic acid molecule in the above descriptions of how to ascertain whether a particular variant, fragment, or derivative is functional may be replaced by references to a codon optimised molecule disclosed herein. As used herein, the term “functional variant” preferably refers to a molecule, e.g., a polypeptide or nucleic acid molecule that retains at least about 70% or more (including at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 97%, at least 99%, or 100%) of the biological activity of a molecule disclosed herein, such as a nucleic acid sequence, a coding sequence, a codon optimised sequence or an amino acid sequence. Biological activity may for instance refer to one or more of activity in a luciferase assay, transcriptomic changes and / or effects on cell conversion. Preferably, a “functional variant” is defined by reference to both sequence identity percentage and biological activity. For instance, a “functional variant” may possess at least 70% (including at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity counted over the full length alignment with the amino acid or nucleotide sequences) and at least about 70% or more (including at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 97%, at least 99%, or 100%) of the biological activity of a molecule disclosed herein, such as a nucleic acid sequence, a coding sequence, a codon optimised sequence or an amino acid sequence. A “functional variant” may possess at least 80% (including at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity counted over the full length alignment with the amino acid or nucleotide sequences) and at least about 80% or more (including at least 85%, at least 90%, at least 95%, at least 97%, at least 99%, or 100%) of the biological activity of a molecule disclosed herein, such as a nucleic acid sequence, a coding sequence, a codon optimised sequence or an amino acid sequence. A “functional variant” may possess at least 90% (including at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity counted over the full length alignment with the amino acid or nucleotide sequences) and at least about 90% or more (including at least 95%, at least 97%, at least 99%, or 100%) of the biological activity of a molecule disclosed herein, such as a nucleic acid sequence, a coding sequence, a codon optimised sequence or an amino acid sequence. A “functional variant” may possess at least 95% (including at least 96%, at least 97%, at least 98%, or at least 99% sequence identity counted over the full length alignment with the amino acid or nucleotide sequences) and at least about 95% or more (including at least 97%, at least 99%, or 100%) of the biological activity of a molecule disclosed herein, such as a nucleic acid sequence, a coding sequence, a codon optimised sequence or an amino acid sequence.

[1085] Variants may comprise one or more amino acid substitutions. Amino acid substitutions are typically conservative substitutions, ie, replacement of one amino acid with another with generally similar properties, such that the overall function is probably not seriously affected. Thus, the amino acids glycine, alanine, valine, leucine and isoleucine can often be substituted for one another (amino acids with aliphatic side chains). Among these potential substitutions, glycine and alanine are used to replace each other (as they have relatively short side chains), valine, leucine and isoleucine replace each other It is preferred that they be used because they have larger aliphatic side chains that are hydrophobic. Other amino acids that can often be substituted for one another are: phenylalanine, tyrosine and tryptophan (amino acids with aromatic side chains); lysine, arginine and histidine (amino acids with basic side chains); aspartic acid and glutamic acid (acidic side) asparagine and glutamine (amino acids with amide side chains); and cysteine and methionine (amino acids with sulphur containing side chains) are included.

[1086] The nucleic acid molecule may be isolated. The nucleic acid molecule may be recombinant. The nucleic acid molecule may be engineered or non-naturally occurring. The terms “isolated”, “recombinant”, “engineered” and “non-naturally occurring”, when referring to a nucleic acid molecule indicate that it is at least substantially free from at least one other component with which they are naturally associated in nature and as found in nature. In addition, the terms can indicate that the nucleic acid molecule has a sequence not found in nature.

[1087] The nucleic acid molecule may be for expression of the at least two transcription factors in a source cell. The nucleic acid molecule may be for expression of the at least two transcription factors in a cochlear source cell. The nucleic acid molecule may be for expression of the at least two transcription factors in an inner ear non-sensory cell. The nucleic acid molecule may be for expression of the at least two transcription factors in a cell type selected from the group consisting of a Dieters’ cell, a pillar cell, a Kolliker’s organ cell, a lesser epithelial ridge cell, an inner phalangeal cell, an inner border cell, a greater epithelial ridge cell, inner sulcus cells and outer sulcus cells. The nucleic acid molecule may be for expression of the at least two transcription factors in a Dieters’ cell, a pillar cell or a Kolliker’s organ cell. The nucleic acid molecule may be for expression of the at least two transcription factors in a Dieters’ cell or a pillar cell.

[1088] The nucleic acid molecule may comprise a promoter. A "promoter" refers to a DNA sequence recognized by the synthetic machinery of the cell, or introduced synthetic machinery, required to initiate the specific transcription of a gene.

[1089] One or more transcription factor may be operably linked to the promoter. The phrase “under transcriptional control” or “operably linked to” means that the promoter is in the correct location and orientation in relation to the nucleic acid to control RNA polymerase initiation of transcription and expression of the gene. A promoter also optionally includes distal enhancer or repressor elements. Any promoter suitable fordriving expression of the transcription factors in source cells, particularly cochlear cells, may be used. For example, the promoter may be a constitutive promoter, an inducible promoter, a cell-specific promoter, a tissue-specific promoter, a cell-selective promoter or a tissue-selective promoter. A “constitutive promoter” is a promoter that is continuously active. Constitutive promoters can therefore allow continuous expression of any operably linked genes. Constitutive promoters may not be subject to regulation be external signals or molecules. For example, constitutive promoters include CAG, CBA, CBh, sCAG, CMV, beta actin, ubiquitin C, PGK, EF1 a, SV40, SFFV, RSV and MMLV. In contrast, the activity of an “inducible promoter” is regulated by an external signal or molecule (for example a transcription factor). A “cell-specific promoter” or “tissue-specific promoter” is a promoter that directs expression of a nucleic acid molecule in particular cells or tissues. Where a promoter preferentially directs expression of a nucleic acid molecule in particular cells or tissues but also directs expression in other cells or tissues at a lower level, it may be referred to as a “cell-selective promoter” or a “tissue-selective promoter”.

[1090] The promoter may comprise an enhancer region and a promoter region. The promoter may further comprise an intron sequence. The enhancer region may be arranged 5’ relative to the promoter region. The intron sequence may be arranged 3’ relative to the promoter region.

[1091] The promoter may comprise a chicken p actin promoter region, or a functional variant thereof. Examples of promoters comprising a chicken actin promoter region include CAG, CBA, CBh and sCAG. The chicken p actin promoter region may refer to the following nucleic acid sequence, identified as SEQ ID NO: 41

[1092] SEQ ID NO: 41

[1093] TCGAGGTGAGCCCCACGTTCTGCTTCACTCTCCCCATCTCCCCCCCCTCCCCACCCCCAATTTTGTAT TTATTTATTTTTTAATTATTTTGTGCAGCGATGGGGGCGGGGGGGGGGGGGGGGCGCGCGCCAGGC GGGGCGGGGCGGGGCGAGGGGCGGGGCGGGGCGAGGCGGAGAGGTGCGGCGGCAGCCAATCA GAGCGGCGCGCTCCGAAAGTTTCCTTTTATGGCGAGGCGGCGGCGGCGGCGGCCCTATAAAAAGC GAAGCGCGCGGCGGGCG

[1094] The promoter may comprise a CMV promoter region, or a functional variant thereof. Examples of promoters comprising a chicken p actin promoter region include CMV1 and CMV2. The CMV promoter region may refer to the following nucleic acid sequence, identified as SEQ ID NO: 42

[1095] SEQ ID NO: 42

[1096] GTGATGCGGTTTTGGCAGTACATCAATGGGCGTGGATAGCGGTTTGACTCACGGGGATTTCCAAGTC TCCACCCCATTGACGTCAATGGGAGTTTGTTTTGGCACCAAAATCAACGGGACTTTCCAAAATGTCGT AACAACTCCGCCCCATTGACGCAAATGGGCGGTAGGCGTGTACGGTGGGAGGTCTATATAAGCAGAG CT

[1097] The promoter may comprise a CMV enhancer region, or a functional variant thereof. Examples of promoters comprising a CMV enhancer region include CAG, CBA, CBh, sCAG, CMV1 and CMV2. The CMV enhancer region may refer to the following nucleic acid sequence, identified as SEQ ID NO: 43 SEQ ID NO: 43

[1098] CGTTACATAACTTACGGTAAATGGCCCGCCTGGCTGACCGCCCAACGACCCCCGCCCATTGACGTCA

[1099] ATAATGACGTATGTTCCCATAGTAACGCCAATAGGGACTTTCCATTGACGTCAATGGGTGGAGTATTTA CGGTAAACTGCCCACTTGGCAGTACATCAAGTGTATCATATGCCAAGTACGCCCCCTATTGACGTCAAT GACGGTAAATGGCCCGCCTGGCATTATGCCCAGTACATGACCTTATGGGACTTTCCTACTTGGCAGTA CATCTACGTATTAGTCATCGCTATTACCATG

[1100] The promoter may comprise CAG, CBA, CBh, sCAG or CMV, or a functional variant thereof. The promoter may consist of or consist essentially of CAG, CBA, CBh, sCAG or CMV, or a functional variant thereof.

[1101] The promoter may comprise CAG, or a functional variant thereof. The promoter may consist of or consist essentially of CAG, or a functional variant thereof. CAG may refer to the following nucleic acid sequence, identified as SEQ ID NO: 44

[1102] SEQ ID NO: 44

[1103] CTCGACATTGATTATTGACTAGTTATTAATAGTAATCAATTACGGGGTCATTAGTTCATAGCCCATATATG

[1104] GAGTTCCGCGTTACATAACTTACGGTAAATGGCCCGCCTGGCTGACCGCCCAACGACCCCCGCCCAT TGACGTCAATAATGACGTATGTTCCCATAGTAACGCCAATAGGGACTTTCCATTGACGTCAATGGGTGG AGTATTTACGGTAAACTGCCCACTTGGCAGTACATCAAGTGTATCATATGCCAAGTACGCCCCCTATTG ACGTCAATGACGGTAAATGGCCCGCCTGGCATTATGCCCAGTACATGACCTTATGGGACTTTCCTACT TGGCAGTACATCTACGTATTAGTCATCGCTATTACCATGGTCGAGGTGAGCCCCACGTTCTGCTTCACT CTCCCCATCTCCCCCCCCTCCCCACCCCCAATTTTGTATTTATTTATTTTTTAATTATTTTGTGCAGCGAT GGGGGCGGGGGGGGGGGGGGGGCGCGCGCCAGGCGGGGCGGGGCGGGGCGAGGGGCGGGGC GGGGCGAGGCGGAGAGGTGCGGCGGCAGCCAATCAGAGCGGCGCGCTCCGAAAGTTTCCTTTTAT GGCGAGGCGGCGGCGGCGGCGGCCCTATAAAAAGCGAAGCGCGCGGCGGGCGGGAGTCGCTGC GCGCTGCCTTCGCCCCGTGCCCCGCTCCGCCGCCGCCTCGCGCCGCCCGCCCCGGCTCTGACTG ACCGCGTTACTCCCACAGGTGAGCGGGCGGGACGGCCCTTCTCCTCCGGGCTGTAATTAGCGCTTG GTTTAATGACGGCTTGTTTCTTTTCTGTGGCTGCGTGAAAGCCTTGAGGGGCTCCGGGAGGGCCCTT TGTGCGGGGGGAGCGGCTCGGGGGGTGCGTGCGTGTGTGTGTGCGTGGGGAGCGCCGCGTGCG GCTCCGCGCTGCCCGGCGGCTGTGAGCGCTGCGGGCGCGGCGCGGGGCTTTGTGCGCTCCGCAG

[1105] TGTGCGCGAGGGGAGCGCGGCCGGGGGCGGTGCCCCGCGGTGCGGGGGGGGCTGCGAGGGGA ACAAAGGCTGCGTGCGGGGTGTGTGCGTGGGGGGGTGAGCAGGGGGTGTGGGCGCGTCGGTCGG GCTGCAACCCCCCCTGCACCCCCCTCCCCGAGTTGCTGAGCACGGCCCGGCTTCGGGTGCGGGGC TCCGTACGGGGCGTGGCGCGGGGCTCGCCGTGCCGGGCGGGGGGTGGCGGCAGGTGGGGGTGC CGGGCGGGGCGGGGCCGCCTCGGGCCGGGGAGGGCTCGGGGGAGGGGCGCGGCGGCCCCCGG AGCGCCGGCGGCTGTCGAGGCGCGGCGAGCCGCAGCCATTGCCTTTTATGGTAATCGTGCGAGAG GGCGCAGGGACTTCCTTTGTCCCAAATCTGTGCGGAGCCGAAATCTGGGAGGCGCCGCCGCACCC CCTCTAGCGGGCGCGGGGCGAAGCGGTGCGGCGCCGGCAGGAAGGAAATGGGCGGGGAGGGCC TTCGTGCGTCGCCGCGCCGCCGTCCCCTTCTCCCTCTCCAGCCTCGGGGCTGTCCGCGGGGGGAC GGCTGCCTTCGGGGGGGACGGGGCAGGGCGGGGTTCGGCTTCTGGCGTGTGACCGGCGGCTCTA GAGCCTCTGCTAACCATGTTCATGCCTTCTTCTTTTTCCTACAGCTCCTGGGCAACGTGCTGGTTATT GTGCTGTCTCATCATTTTGGCAAAGAATTG The promoter may comprise an intron sequence. The intron sequence may be selected from the group consisting of a chimeric chicken p actin I rabbit globin intron sequence; an SV40 intron sequence; a chimeric chicken p actin I minute virus of mice intron sequence; a chicken p actin intron sequence and a chimeric chicken p actin I human p globin intron sequence. A CAG promoter may comprise a chimeric chicken p actin I rabbit p globin intron sequence. A CBA promoter may comprise an SV40 intron sequence. A CBh promoter may comprise a chimeric chicken p actin I minute virus of mice intron sequence. An sCAG promoter may comprise a chicken p actin intron sequence. A CMV1 promoter may comprise a chimeric chicken p actin I human p globin intron sequence. A CMV2 promoter may comprise none of the above intron sequences.

[1106] As used herein, a promoter “for” expression of a gene in source cells, such as cochlear cells, refers to a promoter suitable for expression of the gene in source cells, such as cochlear cells. To be suitable for expression of a gene in cochlear cells, the promoter may be a cochlear cells specific promoter or a cochlear cells selective promoter. Alternatively, to be suitable for expression of a gene in cochlear cells, the promoter may be an inducible promoter a constitutive promoter. A promoter which is specific for a cell type other than cochlear cells, in particular a promoter which is specific for a cochlear cell type other than cochlear support cells, may not be suitable for expression of a gene in cochlear support cells. The promoter may therefore drive a greater level (such as at least a 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30 or 50 fold increase) of expression of the gene in cochlear support cells relative to the level of expression in another cochlear cell type, such as cochlear hair cells.

[1107] The promoter may be a cochlear cell specific promoter or a cochlear cell selective promoter which drives expression in both cochlear support cells and cochlear hair cells. The promoter may preferentially drive expression in one cell type (e.g., cochlear support cells) while retaining a measurable, though reduced, activity in another (e.g., cochlear hair cells). For example, the promoter may drive expression in cochlear support cells at a greater level (such as at least a 1 .5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30 or 50 fold increase) relative to the level of expression in cochlear hair cells, yet still drive expression in cochlear hair cells.

[1108] The promoter may be a synthetic promoter. The promoter may be a synthetic promoter specifically engineered to achieve cell-type-specific expression in both cochlear support cells and cochlear hair cells. In some embodiments, the synthetic promoter may be balanced, driving comparable levels of gene expression in both cochlear support cells and cochlear hair cells. In other embodiments, the promoter may preferentially drive higher expression in one cell type, whilst still sufficient for drive expression in the other cell type. For example, the promoter may drive expression in cochlear support cells at a greater level (such as at least a 1 .5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30 or 50 fold increase) relative to cochlear hair cells, yet still drive expression in cochlear hair cells.

[1109] The nucleic acid molecule may comprise one or more regulatory element. “Regulatory element” includes promoters, enhancers, internal ribosomal entry sites (IRES), and other expression control elements (e.g., transcription termination signals, such as polyadenylation signals and poly-U sequences). Such regulatory elements are described, for example, in Goeddel, Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif (1990), which is hereby incorporated by reference in its entirety. Regulatory elements include those that direct constitutive expression of a nucleotide sequence in many types of source cells and those that direct expression of the nucleotide sequence only in certain source cells (e.g., cell-specific regulatory sequences). Regulatory elements may also direct expression in a temporal-dependent manner, which may or may not also be tissue or cell-type specific.

[1110] The nucleic acid molecule may comprise an enhancer. The enhancer may comprise a Lfng-En3 enhancer element. “Lfng-En3” is a synthetic enhancer element derived from the Lfng (Lunatic fringe) gene locus, specifically engineered to drive gene expression in cochlear supporting cells. It incorporates the third enhancer region (En3) of the Lfng gene, which plays a role in the spatial and temporal regulation of Notch signalling during inner ear development. Lfng-En3 has been shown to confer highly specific expression in cochlear support cells, including pillar cells and Deiters’ cells, while minimizing off-target expression in cochlear hair cells and other non-cochlear tissues. The enhancer may consist of or consist essentially of a Lfng-En3 enhancer element. Lfng-En3 enhancer element sequence may refer to the following nucleic acid sequence, identified as SEQ ID NO: 56.

[1111] SEQ ID NO: 56

[1112] GAAGAGTGTCAGAGCCAGGGAAGCGGGACTGAGCCCTGTGAGGGCTTCTCTACACCACTGTGTAGG TTGTACACTGGCCAAGGTCACACAGGAGATGTATAGCCACACCGTGTGAAACCACAAAGAGGCCACT CCTTCTCTGAAAAGCAGTGGCCCTGGGCAATAGACAGACCTGTGGCAGTCCTGGGGTCCACGTCTT CCTCTGTACTCACTCTAGCTGTGGGTGTTGCTTCACTCCTGACCGTCCAGACAGCCCAGAGGATGCT GGGACCCAGTTTGAAGTCTAGGCTCCAGGGGCAGGCAGGCCAGGCTCTGTCTGACTGGGAGGCCT TGGTTCCCAGGCCATCACAATCGCCACACAACAGGGGTCCCCCGGGAGGGAACCTAATCTTGGGCT ATTGAAGACCTGAAAGCCATGGTCCCTGCCCCAGCAGGCAGACGCGCCTGCCTGCCCCACCTGGGA CACCTGATCCTCCATTGGACCTGCCTCAAAGAGGGACACTGTCCCCCCAGGGTCTCCTGCCCCCAG GCACAGACAAGGAGGGAAACTGGGTCGCAGGGATAGAGTAACAGCAAGGGTTATATTGGATGAGACA GGAGGGAGGGGTGGCCCAGTGTGACAAAGCATTGAGGCTGGGCAGTCTGGAAGAAGACCTTCGGG TCGTGGAGGTGACATAGTCCCAAGATGGCTAATGTGAGCCCCAAGTCTAGACTTACACCACAGATCAT GCTGTAGAGTACTGGGGAGTCAGTAAGACCTATGCACAGCCACTTTCAAACACGGTCCCAAGAGACA CAGCAATTCCTGTGTGCATCCTTGGGCAGGTCCCTCCTTTCCAGCCTCACTCTTCCCGTCTGTGAAAT GAGACTTTAGCCCCAAAGCACTTGGGTACCTTGAACATCTGCAGGGAAGGATTCTATTCAGAAAACCC TCCTCTGTGTTTGGGTGGCTGCCACTATCAGGTACTAGACTGTGTGTAGGGCTGGCGAGGGGACGG GGTAGAGGAGCGTGTACGGAGTAGTAGGACAAACCCAGAAGTCCTGCAGGAGACGGACACTGAGCA TCGAGGCGGAGCCTTCCTGGTAGAGGTGAAGTGTGGAGTGGA

[1113] The nucleic acid molecule may comprise a translation initiation sequence. The translation initiation sequence may be 5’ to the nucleic acid sequence encoding a transcription factor. The translation initiation sequence may be immediately 5’ to start codon, for example ATG, of the nucleic acid sequence encoding a transcription factor. By “immediately” it is meant there may be no nucleotides separating the end of the translation initiation sequence from the start codon of the sequence encoding a transcription factor. The translation initiation sequence may comprise a Kozak sequence. The translation initiation sequence may consist of or consist essentially of a Kozak sequence. Kozak sequence may refer to the following nucleic acid sequence, identified as SEQ ID NO: 45

[1114] SEQ ID NO: 45

[1115] GCCACC

[1116] The nucleic acid may be described as an “expression cassette”. The term "expression cassette" is meant to include any type of genetic construct containing a nucleic acid coding for a gene product in which part or all of the nucleic acid encoding sequence is capable of being transcribed and translated, i.e., is under the control of a promoter. An “exogenous expression cassette” is introduced exogenously, originating from outside the organism. As used herein, the term “nucleic acid” encompasses DNA and RNA. “A nucleic acid” as used herein includes but is not limited to a polynucleotide, protein, oligonucleotide, synthetic mRNA molecule, synthetic RNA molecule (for example, repRNA, also known as saRNA), synthetic DNA molecule, siRNAs, an RNAi and a peptide-nucleic acid (PNA).

[1117] The nucleic acid(s) encoding the transcription factors can be cloned in a monocistronic expression vector, a bicistronic expression vector or a polycistronic expression vector. A monocistronic vector encodes for a single transcription factor, a bicistronic expression vector encodes for two transcription factors and a polycistronic expression vector encodes for more than one transcription factor. In a bicistronic or polycistronic expression vector, the nucleic acid sequences encoding the transcription factors may be separated by a linker, for example, a P2A, T2A, E2A or F2A linker. The linker may induce ribosomal skipping when the protein is being translated so that two or more separate proteins are generated. Alternatively, the nucleic acid sequences encoding the transcription factors may be separated by an internal ribosomal entry site (IRES), such as an IRES derived from the encephalomyocarditis virus (EMCV). The IRES may function by acting as an additional ribosome recruitment site, allowing translation initiation to occur at an internal region of the mRNA in addition to a primary translation initiation site.

[1118] The nucleic acid molecule may therefore comprise a linker sequence separating sequences encoding transcription factors. The linker sequence may comprise an IRES or encodes a 2A family peptide. The 2A family peptide may be selected from the group consisting of P2A, T2A, E2A and F2A. The linker sequence may consist of a P2A, T2A, E2A or F2A linker. The linker sequence may consist essentially of a P2A, T2A, E2Aor F2A linker. The linker sequence may consist of an IRES. The linker sequence may consist essentially of an IRES.

[1119] P2A may refer to the following nucleic acid sequence, identified as SEQ ID NO: 46

[1120] SEQ ID NO: 46

[1121] GGAAGCGGAGCCACGAACTTCTCTCTGTTAAAGCAAGCAGGAGATGTTGAAGAAAACCCCGGGCCT

[1122] Of SEQ ID NO: 46, the first nine nucleotides encode GSG (SEQ ID NO: 51), which is a linker peptide commonly added to 2A sequences to improve cleavage. The linker sequence may encode a 2A family peptide with or without a GSG linker peptide. For example, P2A may alternatively refer to the following nucleic acid sequence, identified as SEQ ID NO: 52

[1123] SEQ ID NO: 52

[1124] GCCACGAACTTCTCTCTGTTAAAGCAAGCAGGAGATGTTGAAGAAAACCCCGGGCCT

[1125] IRES may refer to the following nucleic acid sequence, identified as SEQ ID NO: 47

[1126] SEQ ID NO: 47

[1127] GCCCCTCTCCCTCCCCCCCCCCTAACGTTACTGGCCGAAGCCGCTTGGAATAAGGCCGGTGTGCGT TTGTCTATATGTTATTTTCCACCATATTGCCGTCTTTTGGCAATGTGAGGGCCCGGAAACCTGGCCCTG TCTTCTTGACGAGCATTCCTAGGGGTCTTTCCCCTCTCGCCAAAGGAATGCAAGGTCTGTTGAATGTC GTGAAGGAAGCAGTTCCTCTGGAAGCTTCTTGAAGACAAACAACGTCTGTAGCGACCCTTTGCAGGC AGCGGAACCCCCCACCTGGCGACAGGTGCCTCTGCGGCCAAAAGCCACGTGTATAAGATACACCTG CAAAGGCGGCACAACCCCAGTGCCACGTTGTGAGTTGGATAGTTGTGGAAAGAGTCAAATGGCTCTC CTCAAGCGTATTCAACAAGGGGCTGAAGGATGCCCAGAAGGTACCCCATTGTATGGGATCTGATCTG GGGCCTCGGTGCACATGCTTTACATGTGTTTAGTCGAGGTTAAAAAAACGTCTAGGCCCCCCGAACC ACGGGGACGTGGTTTTCCTTTGAAAAACACGATGATAATATGGCCACAACC

[1128] The nucleic acid molecule may comprise a polyadenylation signal sequence. The polyadenylation signal sequence may be any suitable polyadenylation signal sequence. For example, the polyadenylation signal sequence may be a BGH or a SV40 polyadenylation signal sequence. The BGH polyadenylation signal sequence may refer to the following nucleic acid sequence identified as SEQ ID NO: 53

[1129] SEQ ID NO: 53

[1130] CTGTGCCTTCTAGTTGCCAGCCATCTGTTGTTTGCCCCTCCCCCGTGCCTTCCTTGACCCTGGAAGG TGCCACTCCCACTGTCCTTTCCTAATAAAATGAGGAAATTGCATCGCATTGTCTGAGTAGGTGTCATTC TATTCTGGGGGGTGGGGTGGGGCAGGACAGCAAGGGGGAGGATTGGGAAGAGAATAGCAGGCATG CTGGGGA

[1131] Wherein the nucleic acid molecule encodes a single transcription factor (and may therefore be described as a monocistronic expression vector), the nucleic acid sequence encoding the transcription factor may be 3’ relative to the promoter and / or the nucleic acid sequence encoding the transcription factor may be 5’ relative to the polyadenylation signal sequence. The translation initiation sequence may be 3’ relative to the promoter and 5’ relative to the nucleic acid sequence encoding the transcription factor.

[1132] Wherein the nucleic acid molecule encodes at least two transcription factors (and may therefore be described as a bicistronic or polycistronic expression vector), the nucleic acid sequence encoding a first transcription factor may be 3’ relative to the promoter and / or the nucleic acid sequence encoding the first transcription factor may be 5’ relative to the polyadenylation signal sequence. The nucleic acid sequence encoding a second transcription factor may be 3’ relative to the promoter and / or the nucleic acid sequence encoding the second transcription factor may be 5’ relative to the polyadenylation signal sequence. The nucleic acid sequence encoding the first transcription factor may be 5’ relative to the nucleic acid sequence encoding a second transcription factor. The nucleic acid molecule may comprise a linker sequence which is 3’ relative to the nucleic acid sequence encoding the first transcription factor and / or is 5’ relative to the nucleic acid sequence encoding the second transcription factor. The translation initiation sequence may be 3’ relative to the promoter and 5’ relative to the nucleic acid sequence encoding the transcription factor, typically to the nucleic acid sequence encoding the first transcription factor.

[1133] The nucleic acid sequences encoding the at least two transcription factors may be in any suitable arrangement.

[1134] The first transcription factor may be Gfi1. The second transcription factor may be Pou4f3. The first transcription factor may be Gfi1 and the second transcription factor may be Pou4f3. The nucleic acid sequence encoding Gfi1 may be 5’ relative to the nucleic acid sequence encoding Pou4f3. The promoter may be CAG. The linker sequence may be P2A.

[1135] The first transcription factor may be Lhx3. The second transcription factor may be Six2. The first transcription factor may be Lhx3 and the second transcription factor may be Six2. The nucleic acid sequence encoding Lhx3 may be 5’ relative to the nucleic acid sequence encoding Six2. The promoter may be CAG. The linker sequence may be P2A.

[1136] The first transcription factor may be Isl1 . The second transcription factor may be Kcnip3. The first transcription factor may be Isl1 and the second transcription factor may be Kcnip3. The nucleic acid sequence encoding Isl1 may be 5’ relative to the nucleic acid sequence encoding Kcnip3. The promoter may be CAG. The linker sequence may be P2A.

[1137] The first transcription factor may be Pknox2. The second transcription factor may be Kcnip3. The first transcription factor may be Pknox2 and the second transcription factor may be Kcnip3. The nucleic acid sequence encoding Pknox2 may be 5’ relative to the nucleic acid sequence encoding Kcnip3. The promoter may be CAG. The linker sequence may be P2A.

[1138] The first transcription factor may be Gfi1. The second transcription factor may be Lhx3. The first transcription factor may be Gfi1 and the second transcription factor may be Lhx3. The nucleic acid sequence encoding Gfi 1 may be 5’ relative to the nucleic acid sequence encoding Lhx3. The promoter may be CAG. The linker sequence may be P2A.

[1139] The first transcription factor may be Gfi 1 . The second transcription factor may be Six2. The first transcription factor may be Gfi1 and the second transcription factor may be Six2. The nucleic acid sequence encoding Gfi1 may be 5’ relative to the nucleic acid sequence encoding Six2. The promoter may be CAG. The linker sequence may be P2A.

[1140] Wherein the nucleic acid molecule encodes at least three transcription factors (and may therefore be described as a polycistronic expression vector), the nucleic acid molecule may be arranged substantially as described above in respect of a nucleic acid molecule encoding at least two transcription factors, wherein the nucleic acid molecule further comprises a nucleic acid sequence encoding a third transcription factor. The nucleic acid sequence encoding a third transcription factor may be 3’ relative to the promoter and / or the nucleic acid sequence encoding the third transcription factor may be 5’ relative to the polyadenylation signal sequence. Typically, the nucleic acid sequence encoding a third transcription factor is 3’ relative to the nucleic acid sequence encoding the second transcription factor. The nucleic acid molecule may comprise a further linker sequence which is 3’ relative to the nucleic acid sequence encoding the second transcription factor and / or is 5’ relative to the nucleic acid sequence encoding the third transcription factor.

[1141] The first transcription factor may be Gfi1. The second transcription factor may be Pou4f3. The third transcription factor may be Lhx3. The first transcription factor may be Gfi1 , the second transcription factor may be Pou4f3 and the third transcription factor may be Lhx3. The promoter may be CAG. The linker sequence may be P2A.

[1142] The first transcription factor may be Gfi1. The second transcription factor may be Pou4f3. The third transcription factor may be Six2. The first transcription factor may be Gfi1 , the second transcription factor may be Pou4f3 and the third transcription factor may be Six2. The promoter may be CAG. The linker sequence may be P2A.

[1143] The first transcription factor may be Gfi1. The second transcription factor may be Pou4f3. The third transcription factor may be Lhx3. The fourth transcription factor may be Six2. The first transcription factor may be Gfi1 , the second transcription factor may be Pou4f3, the third transcription factor may be Lhx3 and the fourth transcription factor may be Six2. The promoter may be CAG. The linker sequence may be P2A.

[1144] As used herein, references to “5’ relative to” or “3’ relative to” refer to the direction along a DNA strand in an open reading frame (ORF).

[1145] The nucleic acid molecule may be a self-replicating RNA. A “self-replicating RNA” or “self-amplifying RNA” or“repRNA” or“saRNA” is an RNA that is capable of continuously replicating, as well as transcribing itself, in a host cell as a replicon without the need for a DNA template. Accordingly, a repRNA (also known as saRNA) for inducing inner ear non-sensory cells to transdifferentiate into cochlear hair cells, may comprise a 5’cap and sequences encoding non-structural proteins, sequences encoding at least two or more transcription factors selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, independent ribosome entry sites (IRES), optionally fluorescent marker genes (GFP or mCherry), and 3’poly A tail. The repRNA (also known as saRNA) does not encode Atohl . The repRNA (also known as saRNA) may comprise a promoter operably linked to a nucleic acid sequence encoding at least two or more transcription factors selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3, or a functional variant of any thereof, wherein the promoter is for expression of the two or more transcription factors in inner ear non-sensory cells. Further, the repRNA (also known as saRNA) molecule can comprise two RNA molecules: a first molecule comprising sequences encoding non-structural proteins required for replication of the RNA, and a second molecule comprising a sequence encoding at least two transcription factors. The nucleic acid molecule may be for conversion of a source cell, such as a cochlear source cell, such as an inner ear non-sensory cell, as defined elsewhere herein. The nucleic acid molecule may be for conversion to a target cell, such as a cochlear hair cell or a cochlear hair-like cell, as defined elsewhere herein. The nucleic acid molecule may be for conversion of a source cell, such as a cochlear source cell, such as an inner ear non-sensory cell, to a target cell, such as a cochlear hair cell or a cochlear hair-like cell. For example, the nucleic acid molecule may be for conversion of an inner ear non-sensory cell to a cochlear hair cell or a cochlear hair-like cell.

[1146] According to a second aspect, the invention provides a system for increasing expression of genes encoding at least two transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

[1147] The system may comprise one or more nucleic acid molecules configured when expressed to increase the expression of genes encoding at least two transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl . Alternatively, the system may comprise nucleic acids and / or proteins which when expressed in a cell, increase the expression of genes encoding at least two transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl . The system may comprise a protein or a polypeptide described herein. In such instances, the system may also or alternatively comprise one or more nucleic acid molecules or polynucleotides encoding the corresponding protein or polypeptide. The system may comprise a ribonucleic acid (RNA) molecule described herein. In such instances, the system may also or alternatively comprise one or more deoxyribonucleic acid (DNA) molecules encoding the corresponding RNA.

[1148] It is not excluded that the system may be for increasing expression of genes encoding one or more additional transcription factor not selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. However, the one or more additional transcription factorforwhich the system increases expression may not include Atohl . The system may not be for increasing expression of Atohl . The be for increasing expression of Atohl or a functional variant thereof. The system may not be for increasing expression of an atonal-associated factor. The be for increasing expression of an atonal-associated factor or a functional variant thereof.

[1149] The system may comprise one or more nucleic acid molecules encoding a gene activating protein. The system may comprise a gene activating protein. A gene activating protein is for increasing transcription of a gene and may alternatively be termed a transcriptional activator. The gene activating protein may comprise an activation domain. The gene activating protein and / or the activation domain may be for inducing an increase in gene expression, in particular by direct activation. The gene activating protein may be for binding to a target DNA sequence. The binding to a target DNA sequence may be self-guided or may be guided by an ancillary nucleic acid sequence. Accordingly, the gene activating protein may be a nucleic acid guided gene activating protein or a self-guided gene activating protein.

[1150] The gene activating protein may be a nucleic acid guided gene activating protein. Nucleic acid guided gene activating proteins include the Cas family of proteins. Accordingly, the gene activating protein may be a Cas-based gene activating protein. The gene activating protein may comprise a Cas protein or a Cas fusion protein. The gene activating protein may comprise a Cas protein from the S. pyogenes CRISPR-Cas9 system. Any suitable Cas protein could be used to achieve CRISPR-based gene activation if adjoined to a functional gene activation domain. The system may be a CRISPR activation (CRISPRa) system.

[1151] The Cas protein can be mutated so that the nuclease activity is inactivated. An inactivated Cas9 protein may be termed "ICas9” or "dCas9". An inactivated Cas12 protein may be termed "ICas12” or "dCas12". Exemplary inactivating mutations with reference to the S. pyogenes Cas9 sequence include: D10A, E762A, H840A, N854A, N863A and D986A. Exemplary inactivating mutations with reference to the S. aureus Cas9 sequence include D10A and N580A. The Cas9 may be a mutant S. aureus Cas9. The dCas9 may be a Cas9 molecule that includes at least two mutations selected from the group consisting of D10A, E762A, H840A, N854A, N863A and D986A, with reference to the S. pyogenes Cas9 sequence. The Cas may be a dCas9. The Cas may be a dCas12.

[1152] The gene activating protein may comprise a gene activation domain. The gene activation domain may be fused to the gene activating protein. The gene activation domain may be termed a transactivation domain. The gene activation domain may comprise a herpes simplex virus VP16 transactivation domain or a derivative thereof, such as VP64. The gene activation domain may comprise the composite VPR (VP64, p65, Rta) transactivation domain. The gene activation domain may comprise components ofthe Synergistic Activation Mediator (SAM) system developed forCRISPr / Cas mediated gene activation. For example, gene expression of endogenous mammalian genes, such as human genes, can be achieved by targeting a fusion protein of a first polypeptide domain, such as dCas9 ordCas12 and a transactivation domain to mammalian promoters via combinations of gRNAs. The transactivation domain can include a VP16 protein, multiple VP16 proteins, such as a VP48 domain or VP64 domain, p65 domain of NF kappa B transcription activator, or p300. For example, the fusion protein may be dCas9-VP64. The fusion protein may be VP64-dCas9- VP64. The fusion protein may be dCas9-p300.

[1153] The gene activating protein may be self-guided. Self-guided gene activation proteins include transcription activator-like effector (TALE)-based and a zinc finger (ZNF)-based proteins. The self-guided gene activation protein may be configured to target and / or increase expression of a transcription factor disclosed herein. The system may comprise two or more self-guided gene activation proteins. Each of the two or more self- guided gene activation proteins may be configured to target and / or increase expression of a transcription factor disclosed herein. The system may comprise a first self-guided gene activation protein and a second self-guided gene activation protein. The first self-guided gene activation protein may be for targeting a sequence in the promoter region of a first one ofthe transcription factors, or functional variants thereof. The second self-guided gene activation protein may be for targeting a sequence in the promoter region of a second one of the transcription factors, or functional variants thereof. The first and the second one of the transcription factors, or functional variants thereof, may be different. The system may comprise at least one, at least two, at least three, at least four, at least 5, at least 6, at least 7, at least 8, at least 9 or at least 10 self-guided gene activation protein, each of which may target a different transcription factor, or functional variant thereof.

[1154] The two or more self-guided gene activation proteins may target any two or more transcription factors described as being encoded by the nucleic acid molecule according to the first aspect. For example, the two or more self-guided gene activation proteins may target at least two transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl . As a further example, the at least two transcription factors may comprise:

[1155] (a) Pou4f3 and Gfi1 ;

[1156] (b) Gfi1 and Lhx3;

[1157] (c) Gfi1 and Six2;

[1158] (d) Lhx3 and Six2;

[1159] (e) Isl1 and Kcnip3;

[1160] (f) Pknox2 and Kcnip3;

[1161] (g) Pou4f3, Gfi1 and Lhx3;

[1162] (h) Pou4f3, Gfi1 and Six2;

[1163] (I) Pou4f3, Gfi1 and Kcnip3;

[1164] 0) Pou4f3, Gfi1 , Lhx3 and Six2;

[1165] (k) Pou4f3, Gfi1 , Isl1 and Kcnip3; or

[1166] (l) Pou4f3, Gfi1 , Pknox2 and Kcnip3.

[1167] An indirect effect on Atohl expression cannot be excluded when the system is for the direct targeting of at least two transcription factors selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3. Accordingly, the system is not for directly increasing the protein expression of Atohl . The system may not comprise a self-guided gene activation protein targeting Atohl . While the system may comprise one or more further self-guided gene activation proteins targeting transcription factors not selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, the one or more further self-guided gene activation proteins may not target Atohl .

[1168] A self-guided gene activation protein may bind to a "target region", "target sequence" or "protospacer" of the transcription factor it targets. The self-guided gene activation protein may bind to a "target region", "target sequence" or "protospacer" of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 or Kcnip3. The self-guided gene activation protein may not bind to a "target region", "target sequence" or "protospacer" of Atohl .

[1169] A self-guided gene activation protein may comprise a "targeting sequence" or "targeting portion" or "targeting domain" configured to bind to a "target region", "target sequence" or "protospacer" of the transcription factor it targets. The self-guided gene activation protein may comprise a "targeting sequence" or "targeting portion" or "targeting domain" configured to bind to a "target region", "target sequence" or "protospacer" of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 or Kcnip3. The self-guided gene activation protein may not comprise a "targeting sequence" or "targeting portion" or "targeting domain" configured to bind to a "target region", "target sequence" or "protospacer" of Atohl .

[1170] The ancillary nucleic acid sequence may be for targeting a suitable sequence in the promoter region of the target gene and guiding the gene activating protein to increase transcription of the target gene. For example, a CRISPR / Cas-based system for increasing expression of genes may include gRNA molecules (or sgRNA molecules). The gRNA provides the targeting of a CRISPR / Cas-based system for increasing expression of genes. The gRNA may be a fusion of two non-coding RNAs: a crRNA and a tracrRNA. The nucleic acid sequence may include a crRNA and / or a tracrRNA. The gRNA may for example target a desired DNA sequence by exchanging the sequence encoding a 20 bp protospacer which confers targeting specificity through complementary base pairing with the desired DNA target. gRNA mimics the naturally occurring crRNA:tracrRNA duplex involved in a Type II Effector system. The duplex, which may include, for example, a 42-nucleotide crRNA and a 75-nucleotide tracrRNA, may act as a guide for the dCas9 to bind to the desired DNA sequence. The "target region", "target sequence" or "protospacer" refers to a region of the target gene which the CRISPR / Cas9-based system for increasing expression of genes targets and binds. The portion of the gRNA that targets the target sequence in the genome may be referred to as the "targeting sequence" or "targeting portion" or "targeting domain." "Protospacer" or "gRNA spacer" may refer to the region of the target gene to which the CRISPR / Cas9-based system for increasing expression of genes targets and binds; "protospacer" or "gRNA spacer" may also refer to the portion of the gRNA that is complementary to the targeted sequence in the genome. The gRNA may include a gRNA scaffold. A gRNA scaffold facilitates Cas9 binding to the gRNA and may facilitate activity. The gRNA scaffold is a polynucleotide sequence that follows the portion of the gRNA corresponding to the sequence that the gRNA targets. Together, the gRNA targeting portion and gRNA scaffold may form one polynucleotide. The CRISPR / Cas9-based system for increasing expression of genes may include at least one gRNA, wherein the gRNAs target different DNA sequences. The target DNA sequences may be overlapping. The target sequence or protospacer may be followed by a PAM sequence at the 3' end of the protospacer in the genome. Different Type II systems have differing PAM requirements. For example, the S. pyogenes Type II system uses an "NGG" sequence (SEQ ID NO: 48), where "N" can be any nucleotide. The PAM sequence may be "NGG", where "N" can be any nucleotide. The PAM sequence may be NNGRRT (SEQ ID NO: 49) or NNGRRV (SEQ ID NO: 50). The at least one gRNA molecule can bind and recognize a target region.

[1171] The gRNA molecule may comprise a targeting domain, which is a polynucleotide sequence complementary to the target DNA sequence. The gRNA may comprise a "G" at the 5' end of the targeting domain or complementary polynucleotide sequence. The targeting domain of a gRNA molecule may comprise at least a 10 base pair, at least a 11 base pair, at least a 12 base pair, at least a 13 base pair, at least a 14 base pair, at least a 15 base pair, at least a 16 base pair, at least a 17 base pair, at least a 18 base pair, at least a 19 base pair, at least a 20 base pair, at least a 21 base pair, at least a 22 base pair, at least a 23 base pair, at least a 24 base pair, at least a 25 base pair, at least a 30 base pair, or at least a 35 base pair complementary polynucleotide sequence of the target DNA sequence. The targeting domain of a gRNA molecule may be around 19-25 nucleotides in length. The targeting domain of a gRNA molecule may be around 20 nucleotides in length. The targeting domain of a gRNA molecule may be around 21 nucleotides in length. The targeting domain of a gRNA molecule may be around 22 nucleotides in length. The targeting domain of a gRNA molecule may be around 23 nucleotides in length. The targeting domain of a gRNA molecule may be around 24 nucleotides in length.

[1172] The system may comprise one or more deoxyribonucleic acid molecules together encoding two or more guide nucleic acid sequences. The system may comprise two or more guide nucleic acid sequences. The guide nucleic acid sequences may be RNA sequences. The guide nucleic acid sequences may be nucleic acid molecules, such as RNA molecules. Each of the two or more guide nucleic acid sequences may function as a guide nucleic acid for one of the transcription factors, or functional variants thereof. Accordingly, each of the two or more guide nucleic acid sequences may be for targeting a sequence in the promoter region of one of the transcription factors, or functional variants thereof. Each of the two or more guide nucleic acid sequences may be complementary to a sequence in the promoter region of one of the transcription factors, or functional variants thereof. The system may comprise a first guide nucleic acid sequence and a second guide nucleic acid sequence. The first guide nucleic acid sequence may be for targeting a sequence in the promoter region of a first one of the transcription factors, or functional variants thereof. The second guide nucleic acid sequence may be for targeting a sequence in the promoter region of a second one of the transcription factors, or functional variants thereof. The first and the second one of the transcription factors, or functional variants thereof, may be different. The system may comprise at least one, at least two, at least three, at least four, at least 5, at least 6, at least 7, at least 8, at least 9 or at least 10 guide nucleic acid sequences, each of which may target a different transcription factor, or functional variant thereof.

[1173] The two or more guide nucleic acid sequences may target any two or more transcription factors described as being encoded by the nucleic acid molecule according to the first aspect. For example, the two or more guide nucleic acid sequences may target at least two transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl . As a further example, the at least two transcription factors may comprise:

[1174] (a) Pou4f3 and Gfi1 ;

[1175] (b) Gfi1 and Lhx3;

[1176] (c) Gfi1 and Six2;

[1177] (d) Lhx3 and Six2;

[1178] (e) Isl1 and Kcnip3;

[1179] (f) Pknox2 and Kcnip3;

[1180] (g) Pou4f3, Gfi1 and Lhx3;

[1181] (h) Pou4f3, Gfi1 and Six2;

[1182] (I) Pou4f3, Gfi1 and Kcnip3;

[1183] 0) Pou4f3, Gfi1 , Lhx3 and Six2;

[1184] (k) Pou4f3, Gfi1 , Isl1 and Kcnip3; or

[1185] (l) Pou4f3, Gfi1 , Pknox2 and Kcnip3.

[1186] An indirect effect on Atohl expression cannot be excluded when the system is for the direct targeting of at least two transcription factors selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3. Accordingly, the system is not for directly increasing the protein expression of Atohl . The system may not comprise a guide nucleic acid sequence targeting Atohl . While the system may comprise one or more further guide nucleic acid sequences targeting transcription factors not selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, the one or more further guide nucleic acid sequences may not target Atohl .

[1187] A guide nucleic acid sequence may bind to a "target region", "target sequence" or "protospacer" of the transcription factor it targets. The guide nucleic acid sequence may bind to a "target region", "target sequence" or "protospacer" of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 or Kcnip3. The guide nucleic acid sequence may not bind to a "target region", "target sequence" or "protospacer" of Atohl .

[1188] A guide nucleic acid sequence may comprise a "targeting sequence" or "targeting portion" or "targeting domain" configured to bind to a "target region", "target sequence" or "protospacer" of the transcription factor it targets. The guide nucleic acid sequence may comprise a "targeting sequence" or "targeting portion" or "targeting domain" configured to bind to a "target region", "target sequence" or "protospacer" of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 or Kcnip3. The guide nucleic acid sequence may not comprise a "targeting sequence" or "targeting portion" or "targeting domain" configured to bind to a "target region", "target sequence" or "protospacer" of Atohl .

[1189] The gene activating protein may be a nucleic acid guided gene activating protein and the system may further comprise:

[1190] (a) one or more deoxyribonucleic acid molecules together encoding two or more guide nucleic acid sequences, optionally gRNA sequences, or

[1191] (b) two or more guide nucleic acid sequences, optionally gRNA sequences, wherein the each of the two or more guide nucleic acid sequences targets a transcription factor selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, and wherein each of the two or more guide nucleic acid sequences targets a different transcription factor.

[1192] The number of gRNA molecules encoded by a nucleic acid molecule or a vector (e.g., an AAV vector) can be at least 1 gRNA, at least 2 different gRNA, at least 3 different gRNA, at least 4 different gRNA, at least 5 different gRNA, at least 6 different gRNA, at least 7 different gRNA, at least 8 different gRNA, at least 9 different gRNA or at least 10 different gRNAs. The nucleic acid molecule or vector (e.g., an AAV vector) may encode at least one gRNA molecule, i.e., a first gRNA molecule, and optionally a Cas9 molecule. A first nucleic acid molecule or vector (e.g., a first AAV vector) may encodes a gRNA molecule, i.e., a first gRNA molecule, and optionally a Cas9 molecule, and a second nucleic acid molecule or vector (e.g., a second AAV vector) may encodes a gRNA molecule, i.e., a second gRNA molecule, and optionally a Cas9 molecule.

[1193] The nucleic acid sequence encoding the gene activating protein may be split across more than one vector. The full nucleic acid sequence may then be reconstituted in cells that receive both vectors. The full gene activating protein may then be expressed in cells that receive both vectors. This may be advantageous when the size of the nucleic acid sequence encoding the gene activating protein exceeds the cargo capacity of the vector. For example, the nucleic acid sequence encoding a Cas-based gene activating protein may exceed the cargo capacity of an AAV vector. The nucleic acid sequence encoding the Cas-based gene activating protein may therefore be split across more than one AAV.

[1194] The system may comprise:

[1195] (a) a nucleic acid molecule encoding a Cas-based gene activating protein; and

[1196] (b) two or more guide nucleic acid molecules that target at least two transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl and wherein each of the two or more guide nucleic acid molecules targets a different transcription factor.

[1197] The system may comprise:

[1198] (a) a nucleic acid molecule encoding a Cas-based gene activating protein; and

[1199] (b) one or more nucleic acid molecules together encoding two or more guide nucleic acid sequences that target at least two transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl and wherein each of the two or more guide nucleic acid sequences targets a different transcription factor.

[1200] One or more of the one or more nucleic acid molecules together encoding two or more guide nucleic acid sequences may be the same as the nucleic acid molecule encoding a Cas-based gene activating protein. In other words, the one or more guide nucleic acid sequence may be encoded by the same nucleic acid molecule that encodes the Cas-based gene activating protein. Alternatively, the one or more nucleic acid molecules together encoding two or more guide nucleic acid sequences may be different to the nucleic acid molecule encoding a Cas-based gene activating protein.

[1201] Once operational in a cell, the system may be an in vitro system, an ex vivo or an in vivo system, depending on the context of the cell. If the cell is isolated, the system may be an in vitro system. If the cell is part of a tissue that has been removed from a patient, the system may be an ex vivo system. If the cell is part of the body of a patient, the system may be an in vivo system. The system may also refer to a composition of matter to be delivered to a cell in order to increase the expression of genes once the system is operational in the cell. The composition of matter to be delivered to a cell may take various forms, which may in part depend on whether the cell is in vitro, ex vivo or in vivo. In vivo delivery of CRISPR-Cas9 therapeutics has been reviewed in Behr et al (Acta Pharm Sin B. 2021 Aug; 11 (8): 2150-2171), hereby incorporated by reference in its entirety. The present disclosure encompasses any suitable arrangement of the system to enable the system to be delivered to a cell and increase the expression of genes once the system is operational in the cell.

[1202] According to a third aspect, the invention provides a vector comprising the nucleic acid molecule according to the first aspect or the system comprising one or more nucleic acid molecules according to the second aspect. The nucleic acid molecule or molecules can be delivered by a vector such as a viral or a non-viral vector.

[1203] The vector may be a viral vector. The viral vector may be selected from the group consisting of an adeno- associated virus (AAV) vector, a lentiviral vector, a Sendai vector, a Herpes simplex virus (HSV) vector, an Adenoviral vector, an episomal vector and a retroviral vector. The viral vector may be selected from the group consisting of an adeno-associated virus (AAV) vector, a lentiviral vector and an Adenoviral vector. The viral vector may be a lentiviral vector. The viral vector may be an AAV vector.

[1204] A viral vector may be one that integrates into the host cell genome (“integrating” or “integrative”) or one that does not integrate into the host cell genome (“non-integrating” or “non-integrative”). The viral vector may for instance be selected from the group consisting of lentiviruses, Sendai vectors, Herpes simplex virus (HSV), adenoviruses, adeno-associated viruses (AAV), episomal vectors (e.g. EBV vectors) and retroviruses.

[1205] The viral vector may be an integrating viral vector. The viral vector may be an integrating viral vector selected from the group consisting of a lentivirus or a retrovirus.

[1206] The viral vector may be a non-integrating viral vector. The viral vector may be a non-integrating viral vector selected from the group consisting of an AAV, an adenovirus, a Sendai virus, a HSV or an episomal vector.

[1207] The viral vector may be an adenovirus, such as Ad5.

[1208] The viral vector may be engineered to enhance gene delivery. For example, AAVs capsids can be engineered to enhance gene delivery. Capsid variants can be selected to drive protein expression in source cells, for example, cochlear cells.

[1209] The viral vector may comprise a capsid for transduction of source cells. The viral vector may comprise a capsid for transduction of cochlear cells. The viral vector may comprise a capsid for transduction of cochlear support cells. The viral vector may comprise a capsid for transduction of an inner ear non-sensory cell. The viral vector may comprise a capsid for transduction of a cell type selected from the group consisting of a Dieters’ cell, a pillar cell, a Kolliker’s organ cell, a lesser epithelial ridge cell, an inner phalangeal cell, an inner border cell, a greater epithelial ridge cell, inner sulcus cells and outer sulcus cells. The viral vector may comprise a capsid for transduction of a Dieters’ cell, a pillar cell or a Kolliker’s organ cell. The viral vector may comprise a capsid for transduction of a Dieters’ cell or a pillar cell.

[1210] The viral vector may comprise a capsid exhibiting cochlear tropism. The viral vector may comprise a capsid exhibiting tropism for cochlear cells. The viral vector may comprise a capsid exhibiting tropism for cochlear support cells. The viral vector may comprise a capsid exhibiting tropism for an inner ear non-sensory cell. The viral vector may comprise a capsid exhibiting tropism for a cell type selected from the group consisting of a Dieters’ cell, a pillar cell, a Kolliker’s organ cell, a lesser epithelial ridge cell, an inner phalangeal cell, an inner border cell, a greater epithelial ridge cell, inner sulcus cells and outer sulcus cells. The viral vector may comprise a capsid exhibiting tropism for a Dieters’ cell, a pillar cell or a Kolliker’s organ cell. The viral vector may comprise a capsid exhibiting tropism for a Dieters’ cell or a pillar cell.

[1211] The viral vector may comprise a capsid selected from the group consisting of AAV-ShH10, AAV9, AAV1 , AAV2, AAV5, AAV7, AAV8, AAV2 / 1 , AAV2 / 2, AAV2 / 5, AAV2 / 7, AAV2 / 8, AAV2 / 9, AAV-DJ, AAV-ie, AAV- 2.7m8, Anc80L65 and AAV-KP1 .

[1212] The viral vector may comprise a capsid selected from the group consisting of AAV-ShH10, AAV9, AAV1 , AAV2, AAV5, AAV7 and AAV8.

[1213] The viral vector may comprise a capsid selected from the group consisting of AAV-ShH10, AAV9, AAV1 , AAV2 and AAV8, each of which has been reported to transduce pillar cells.

[1214] The viral vector may comprise a capsid selected from the group consisting of AAV-ShH10, AAV9, AAV1 , AAV2, AAV5, AAV7 and AAV8, each of which has been reported to transduce Claudius cells.

[1215] The viral vector may comprise a capsid selected from the group consisting of AAV-ShH10, AAV9, AAV1 and AAV2, each of which has been reported to transduce Dieters cells.

[1216] The viral vector may comprise an AAV2-based pseudotyped serotype. The viral vector may be capsid selected from the group consisting of AAV2 / 1 , AAV2 / 2, AAV2 / 5, AAV2 / 7, AAV2 / 8 and AAV2 / 9.

[1217] The viral vector may comprise a capsid selected from the group consisting of AAV-DJ, AAV-ie, AAV-2.7m8, Anc80L65 and AAV-KP1 . The viral vector may comprise an AAV-DJ capsid.

[1218] “AAV-DJ” is described in Grimm et al. J Virol. 2008;82:5887-5911. It was generated by a gene shuffling approach and is a chimera of AAV-2, AAV-8 and AAV-9. It shares greater than 85% sequence identity to the parental strains, differing from its closest relative (AAV-2) by 60 capsid amino acids (8%). It has been reported to transduce cochlear supporting cells with a high efficiency (Tan et al. Nat Commun. 2019 Aug 19;10(1):3733).

[1219] “AAV-inner ear” (AAV-ie) is described in Tan et al. Nat Commun. 2019 Aug 19;10(1) :3733. It was made by inserting a cell-penetrating peptide-like peptide a CPP-like peptide into the VP1 capsid of AAV-DJ. It is reported to transduce cochlear supporting cells (SCs) with high efficiency and after AAV-ie-mediated transfer of Atohl gene, it is reported that many SCs trans-differentiated into new HCs.

[1220] “ AAV-2.7m8” is described in Dalkara et al. Sci. Transl. Med.5,189ra76-189ra76 (2013). It was made by in vivo directed evolution with the intention of generating an AAV for therapeutic outer retinal gene delivery. It is most closely related to AAV2, with a 9 amino acid insertion relative to AAV2. It has since been reported to be a powerful viral vector for inner ear gene therapy (Isgrig et al. Nat. Commun. 2019 Jan 25;10(1):427). “Anc80L65” is described in Zinn et al. Cell Rep. 2015 Aug 11 ;12(6):1056-68. It was made following an in silico reconstruction of the viral evolutionary lineage. It differs by 8.7% from the corresponding AAV8 sequence and by 12% from the corresponding AAV2 sequence. It has also been reported to be suitable for inner ear gene therapy (Isgrig et al. Nat. Commun. 2019 Jan 25;10(1):427).

[1221] “AAV-KP1 ” is described in Pekrun et al. JCI Insight. 2019 Nov 14; 4(22): e131610. It is a further example of a chimeric capsid. It shares around 92% sequence identity to AAV3B, which is its closest parental strain. AAV-KP1 has been reported to exhibit a tropism for cochlear support cells (Aaron et al. Mol Ther Methods Clin Dev. 2023 Aug 11 :30:413-428).

[1222] “AAV9” is a naturally occurring AAV serotype originally isolated from human tissues. It belongs to Clade F of the AAV family and is closely related to AAV2 and AAV3. AAV9 is well known for its ability to cross the blood-brain barrier and its broad tissue tropism, including skeletal muscle, heart, and liver. It has also been reported to transduce various cell types in the cochlea, including pillar cells and Claudius cells, making it a useful vector for inner ear gene therapy applications (Klimczak et al. PloS one vol. 4,10 e7467. 14 Oct. 2009, doi:10.1371 / journal. pone.0007467).

[1223] “AAV-ShH10” is a synthetic AAV variant. It was developed by directed evolution ofAAV6 capsids to improve transduction efficiency of Muller glia in the retina. AAV-ShH10 differs from its parental AAV6 capsid by several amino acid substitutions that enhance its glial cell specificity. More recently, AAV-ShH10 has been shown to efficiently transduce cochlear support cells, including pillar cells, Deiters’ cells, and Claudius cells, highlighting its potential for targeted gene delivery in the inner ear (Tao et al. Signal transduction and targeted therapy vol. 7,1 109. 22 Apr. 2022, doi:10.1038 / s41392-022-00938-8).

[1224] The vector may be a non-viral vector. Non-viral vectors include but are not limited to liposomes, nanoparticles, exosomes, virus-like particles (VLPs), lipid nanoparticles (LNPs), naked DNA, plasmids, transposons and other means to deliver a nucleic acid molecule into a cell. The non-viral vector may be selected from the group consisting of a liposome, nanoparticle, naked DNA, plasmid and a transposon. Another type of non-viral vector includes RNA molecules, for example mRNA and stabilised RNA, to carry coding genetic information to the cells. The non-viral vector may be a repRNA vector (also known as a saRNA vector), mRNA or stabilised RNA. The non-viral vector may be selected from the group consisting of a liposome, a nanoparticle, an exosome, a virus-like particle (VLP), a lipid nanoparticle (LNP), naked DNA, a plasmid, a transposon, a repRNA vector (also known as a saRNA vector), mRNA and stabilised RNA.

[1225] In some embodiments, the non-viral vector is a repRNA vector (also known as a saRNA vector). The repRNA vector (also known as a saRNA vector) may be generated using any suitable technique. Appropriate techniques are known in the art and exemplified herein. By way of non-limiting example, a repRNA vector may be synthesised in vitro using a DNA template encoding the replicon sequence, followed by transcription. The resulting RNA may be capped, purified, and formulated for delivery using any methods appropriate to the intended application. For example, the repRNA vector (also known as a saRNA vector) may be generated using a plasmid DNA template comprising an alphavirus-based replicon. The replicon may be derived from the Venezuelan Equine Encephalitis Virus (VEEV) strain TC-83 genome. The replicon may comprise viral non-structural protein coding sequences but lacks structural protein coding sequences to prevent production of infectious viral particles. The replicon may be flanked by a T7 promoter at the 5’-end, viral 5’- and 3’-cis active sequences, and a synthetic polyadenylation sequence at the 3’-end. The plasmid template may further comprise a multiple cloning site inserted immediately after the viral 26S subgenomic promoter to enable expression of target open reading frames. The plasmid template may be modified by restriction enzyme cloning to express one or more transcription factors. The saRNA may be generated by in vitro transcription from the plasmid DNA template.

[1226] The nucleic acid molecule or molecules may be delivered using any suitable vector, including viral and non- viral vectors. The present inventors have demonstrated that delivery can be achieved using a variety of platforms, such as an adeno-associated virus (AAV) vector as an example of a viral delivery system, and a self-amplifying RNA (saRNA), also referred to as replicon RNA (repRNA), as an example of a non-viral delivery system.

[1227] The terms “vector” and “expression vector” are used interchangeably herein. The term “vector” may also be interchanged with the term “vehicle”.

[1228] Wherein the vector comprises the system according to the second aspect, a vector comprising the gene activating protein, such as the Cas-based gene activating protein, may comprise the gene activating protein, a deoxyribonucleic acid sequence encoding the gene activating protein, a mRNA sequence encoding the gene activating protein, or a viral genome encoding the gene activating protein.

[1229] Wherein the vector comprises the system according to the second aspect, a vector comprising the guide nucleic acid sequence, such as the gRNA molecule, may comprise the guide nucleic acid sequence itself (such as the gRNA molecule), a deoxyribonucleic acid sequence encoding the guide nucleic acid sequence, a mRNA sequence encoding the guide nucleic acid sequence, or a viral genome encoding the guide nucleic acid sequence.

[1230] Wherein the vector comprises the system according to the second aspect, the vector may comprise the gene activating protein and / or the guide nucleic acid sequence. For example, the vector may comprise the Cas-based gene activating protein and one or more gRNA. The vector may comprise a Cas9 / gRNA ribonucleoprotein (RNP) complex.

[1231] It is not excluded that the vector may further comprise one or more further nucleic acid molecule encoding one or more additional transcription factor not selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. However, the one or more further nucleic acid molecule may not encode Atohl or a functional variant thereof. It is not excluded that the vector may further comprise one or more further nucleic acid molecule for increasing expression of one or more genes encoding one or more additional transcription factor not selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3. However, the one or more further nucleic acid molecule may not be for increasing expression of Atohl or a functional variant thereof.

[1232] According to a fourth aspect, the invention provides a composition comprising the nucleic acid molecule according to the first aspect, the system comprising one or more nucleic acid molecules according to the second aspect or the vector according to the third aspect, and a pharmaceutically acceptable carrier.

[1233] Pharmaceutically acceptable carriers suitable for the delivery of compositions of the present invention and methods for their preparation will be readily apparent to those skilled in the art.

[1234] It is not excluded that the composition may further comprise one or more further nucleic acid molecule encoding one or more additional transcription factor not selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. However, the one or more further nucleic acid molecule may not encode Atohl or a functional variant thereof.

[1235] It is not excluded that the composition may further comprise one or more further nucleic acid molecule for increasing expression of one or more genes encoding one or more additional transcription factor not selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3. However, the one or more further nucleic acid molecule may not be for increasing expression of Atohl or a functional variant thereof.

[1236] According to a fifth aspect, the invention provides a product comprising

[1237] (a) a first nucleic acid molecule, encoding at least one transcription factor, or a functional variant thereof, selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, and

[1238] (b) a second nucleic acid molecule, encoding at least one transcription factor, or a functional variant thereof, selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3; wherein the first nucleic acid molecule and the second nucleic acid molecule each encode different transcription factors and wherein the product does not comprise a nucleic acid molecule encoding Atohl ; as a combined preparation for simultaneous, separate or sequential use in the treatment of hearing loss.

[1239] The product may comprise two or more nucleic acid molecules that between them encode two or more transcription factors, or functional variants thereof, selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. The product may comprise two or more nucleic acid molecules that between them encode two or more transcription factors selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. The product may comprise two or more nucleic acid molecules that between them encode any two or more transcription factors, or functional variants thereof, described elsewhere herein. For example, the transcription factors may comprise:

[1240] (a) Pou4f3 and Gfi1 ;

[1241] (b) Gfi1 and Lhx3;

[1242] (c) Gfi1 and Six2;

[1243] (d) Lhx3 and Six2;

[1244] (e) Isl1 and Kcnip3;

[1245] (f) Pknox2 and Kcnip3;

[1246] (g) Pou4f3, Gfi1 and Lhx3;

[1247] (h) Pou4f3, Gfi1 and Six2;

[1248] (I) Pou4f3, Gfi1 and Kcnip3;

[1249] 0) Pou4f3, Gfi1 , Lhx3 and Six2;

[1250] (k) Pou4f3, Gfi1 , Isl1 and Kcnip3; or

[1251] (l) Pou4f3, Gfi1 , Pknox2 and Kcnip3.

[1252] It is not excluded that the product, such as the first or second nucleic acid molecule, may encode comprise one or more further transcription factor not selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3. However, the product, such as the first or second nucleic acid molecule, may not encode Atohl or a functional variant thereof.

[1253] At least one of the first nucleic acid molecule and the second nucleic acid molecule may encode Pou4f3 and Gfl1 , or functional variants thereof. The first nucleic acid molecule may encode Pou4f3 and Gfl1 . Alternatively, the second nucleic acid molecule may encode Pou4f3 and Gfl1 .

[1254] The first nucleic acid molecule may encode Pou4f3 and Gfi 1 , or functional variants thereof, and the second nucleic acid molecule may encode at least two transcription factors, or functional variants thereof, selected from the group consisting of Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. The first nucleic acid molecule may encode Pou4f3 and Gfl1 and the second nucleic acid molecule may encode at least two transcription factors selected from the group consisting of Lhx3, Isl1 , Six2, Pknox2 and Kcnip3.

[1255] At least one of the first nucleic acid molecule and the second nucleic acid molecule may encode Pou4f3 and Gfi1 , or functional variants thereof, and the other of the first nucleic acid molecule and the second nucleic acid molecule may encode Lhx3 and Six2, or functional variants thereof. The first nucleic acid molecule may encode Pou4f3 and Gfi1 and the second nucleic acid molecule may encode Lhx3 and Six2, or vice versa.

[1256] In some instances,

[1257] (a) the first nucleic acid molecule comprises a nucleic acid sequence encoding Pou4f3, or a functional variant thereof, and a nucleic acid sequence encoding Gfl1 , or a functional variant thereof, and / or

[1258] (b) the second nucleic acid molecule comprises a nucleic acid sequence encoding Lhx3, or a functional variant thereof, and a nucleic acid sequence encoding Six2, or a functional variant thereof. In some instances,

[1259] (a) the first nucleic acid molecule comprises a nucleic acid sequence encoding Pou4f3 and a nucleic acid sequence encoding Gfl1 , and

[1260] (b) the second nucleic acid molecule comprises a nucleic acid sequence encoding Lhx3 and a nucleic acid sequence encoding Six2.

[1261] At least one of the first nucleic acid molecule and the second nucleic acid molecule may encode Pou4f3 and Gfi1 , or functional variants thereof, and the other of the first nucleic acid molecule and the second nucleic acid molecule may encode Isl1 and Kcnip3, or functional variants thereof. The first nucleic acid molecule may encode Pou4f3 and Gfi 1 and the second nucleic acid molecule may encode Isl 1 and Kcnip3, or vice versa.

[1262] In some instances,

[1263] (a) the first nucleic acid molecule comprises a nucleic acid sequence encoding Pou4f3, or a functional variant thereof, and a nucleic acid sequence encoding Gfl1 , or a functional variant thereof, and / or

[1264] (b) the second nucleic acid molecule comprises a nucleic acid sequence encoding Isl1 , or a functional variant thereof, and a nucleic acid sequence encoding Kcnip3, or a functional variant thereof.

[1265] In some instances,

[1266] (a) the first nucleic acid molecule comprises a nucleic acid sequence encoding Pou4f3 and a nucleic acid sequence encoding Gfl1 , and

[1267] (b) the second nucleic acid molecule comprises a nucleic acid sequence encoding Isl1 and a nucleic acid sequence encoding Kcnip3.

[1268] At least one of the first nucleic acid molecule and the second nucleic acid molecule may encode Pou4f3 and Gfi1 , or functional variants thereof, and the other of the first nucleic acid molecule and the second nucleic acid molecule may encode Pknox2 and Kcnip3, or functional variants thereof. The first nucleic acid molecule may encode Pou4f3 and Gfi1 and the second nucleic acid molecule may encode Pknox2 and Kcnip3, or vice versa.

[1269] In some instances,

[1270] (a) the first nucleic acid molecule comprises a nucleic acid sequence encoding Pou4f3, or a functional variant thereof, and a nucleic acid sequence encoding Gfl1 , or a functional variant thereof, and / or

[1271] (b) the second nucleic acid molecule comprises a nucleic acid sequence encoding Pknox2, or a functional variant thereof, and a nucleic acid sequence encoding Kcnip3, or a functional variant thereof.

[1272] In some instances,

[1273] (a) the first nucleic acid molecule comprises a nucleic acid sequence encoding Pou4f3 and a nucleic acid sequence encoding Gfl1 , and

[1274] (b) the second nucleic acid molecule comprises a nucleic acid sequence encoding Pknox2 and a nucleic acid sequence encoding Kcnip3. The first nucleic acid molecule and / or the second nucleic acid molecule may be a nucleic acid molecule according to the first aspect of the invention, wherein the first nucleic acid molecule and the second nucleic acid molecule each encode different transcription factors. The first nucleic acid molecule may be a nucleic acid molecule according to the first aspect of the invention. The second nucleic acid molecule may be a nucleic acid molecule according to the first aspect of the invention.

[1275] The first and / or second nucleic acid molecule may be in the form of a vector or a composition. For example, the first nucleic acid molecule may be in the form of a vector of the third aspect of the invention or in the form of a composition of the fourth aspect of the invention. Likewise, the second nucleic acid molecule may be in the form of a vector of the third aspect of the invention or in the form of a composition of the fourth aspect of the invention. Any one or more of the Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and / or Kcnip3 may be replaced by a functional variant thereof.

[1276] The first nucleic acid molecule and / or the second nucleic acid molecule may be comprised in a vector according to the third aspect of the invention, wherein the first nucleic acid molecule and the second nucleic acid molecule each encode different transcription factors. The first nucleic acid molecule may be comprised in a vector according to the third aspect of the invention. The second nucleic acid molecule may be comprised in a vector according to the third aspect of the invention.

[1277] The product may comprise a third nucleic acid molecule. For instance, the first, second and third nucleic acid molecules may between them encode three or more transcription factors selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. The first, second and third nucleic acid molecules may between them encode:

[1278] (a) Pou4f3, Gfi1 and Lhx3;

[1279] (b) Pou4f3, Gfi1 and Six2;

[1280] (c) Pou4f3, Gfi1 and Kcnip3;

[1281] (d) Pou4f3, Gfi1 , Lhx3 and Six2;

[1282] (e) Pou4f3, Gfi1 , Isl1 and Kcnip3; or

[1283] (f) Pou4f3, Gfi1 , Pknox2 and Kcnip3.

[1284] The third nucleic acid molecule may be in the form of a vector or a composition. For example, the third nucleic acid molecule may be in the form of a vector of the third aspect of the invention or in the form of a composition of the fourth aspect of the invention. Likewise, the third nucleic acid molecule may be in the form of a vector of the third aspect of the invention or in the form of a composition of the fourth aspect of the invention. Any one or more of the Pou4f3, Gfi 1 , Lhx3, Isl 1 , Six2, Pknox2 and / or Kcnip3 may be replaced by a functional variant thereof.

[1285] The third nucleic acid molecule may be comprised in a vector according to the third aspect of the invention, wherein the first nucleic acid molecule, the second nucleic acid molecule and the third nucleic acid molecule each encode different transcription factors. The third nucleic acid molecule may be comprised in a vector according to the third aspect of the invention. The product may comprise a fourth nucleic acid molecule. For instance, the first, second, third and fourth nucleic acid molecules may between them encode four or more transcription factors selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. The first, second, third and fourth nucleic acid molecules may between them encode:

[1286] (a) Pou4f3, Gfi1 , Lhx3 and Six2;

[1287] (b) Pou4f3, Gfi1 , Isl1 and Kcnip3; or

[1288] (c) Pou4f3, Gfi1 , Pknox2 and Kcnip3.

[1289] The fourth nucleic acid molecule may be in the form of a vector or a composition. For example, the fourth nucleic acid molecule may be in the form of a vector of the third aspect of the invention or in the form of a composition of the fourth aspect of the invention. Likewise, the fourth nucleic acid molecule may be in the form of a vector of the third aspect of the invention or in the form of a composition of the fourth aspect of the invention. Any one or more of the Pou4f3, Gfi 1 , Lhx3, Isl 1 , Six2, Pknox2 and / or Kcnip3 may be replaced by a functional variant thereof.

[1290] The fourth nucleic acid molecule may be comprised in a vector according to the third aspect of the invention, wherein the first nucleic acid molecule, the second nucleic acid molecule, the third nucleic acid molecule and the fourth nucleic acid molecule each encode different transcription factors. The fourth nucleic acid molecule may be comprised in a vector according to the third aspect of the invention.

[1291] The first, second, third or fourth nucleic acid molecule may together encode two or more of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and / or Kcnip3 in any combination. The first, second, third or fourth nucleic acid molecule may encode a functional variant of a transcription factor disclosed herein, typically in place of the corresponding transcription factor. The first, second, third or fourth nucleic acid molecule may encode a functional variant of one or more of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and / or Kcnip3 in any combination. The first, second, third or fourth nucleic acid molecule may together encode one or more of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and / or Kcnip3 in any combination and / or a functional variant of one or more of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and / or Kcnip3 in any combination.

[1292] The product may optionally further comprise instructions for the simultaneous, sequential or separate administration of the preparations to a subject in need thereof.

[1293] It is to be appreciated that all references herein to treatment include curative, palliative and prophylactic treatment; although in the context of the invention references to preventing are more commonly associated with prophylactic treatment. Treatment may also include arresting progression in the severity of a disease.

[1294] The treatment of mammals, particularly humans, is preferred. However, both human and veterinary treatments are within the scope of the invention. Accordingly, the product may be for simultaneous, separate or sequential use in the treatment of hearing loss in a mammal. The product may be for simultaneous, separate or sequential use in the treatment of hearing loss in a non-human mammal, such as a mouse, a guinea pig, a dog, a cat or a horse. The product may be for simultaneous, separate or sequential use in the treatment of hearing loss in a human.

[1295] The treatment may comprise administration by any suitable route. The administration may be to a cochlea of the subject. The administration may be to one or more cochlea of the subject. The administration to the subject may be systemic. Administration to the cochlea may have advantages of lower probabilities of off- target delivery, unwanted side effects, toxicity, or blood cochlea barrier / blood-labyrinthine barrier restricted transport. Administration to the cochlea may be by round-window membrane diffusion, round-window membrane injection, cochleostomy, or canalostomy.

[1296] The term “combination”, or terms “in combination”, “used in combination with” or “combined preparation” as used herein may refer to the combined administration of two or more agents simultaneously, sequentially or separately.

[1297] The term “simultaneous” as used herein means that the agents are administered concurrently, i.e. at the same time.

[1298] The term “sequential” as used herein means that the agents are administered one after the other.

[1299] The term “separate” as used herein means that the agents are administered independently of each other but within a time interval that allows the agents to show a combined, preferably synergistic, effect. Thus, administration “separately” may permit one agent to be administered, for example, within 1 minute, 5 minutes or 10 minutes after the other.

[1300] According to a sixth aspect, the invention provides a product comprising

[1301] (a) a first nucleic acid molecule, configured to target for upregulation at least one transcription factor, or a functional variant thereof, selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3, and

[1302] (b) a second nucleic acid molecule, configured to target for upregulation at least one transcription factor, or a functional variant thereof, selected from the group consisting of Pou4f3, Gfi 1 , Lhx3, Isl 1 , Six2, Pknox2 and Kcnip3; wherein the first nucleic acid molecule and the second nucleic acid molecule are each configured to target for upregulation different transcription factors and wherein the product does not comprise a nucleic acid molecule configured to target Atohl for upregulation; as a combined preparation for simultaneous, separate or sequential use in the treatment of hearing loss.

[1303] The product may comprise any nucleic acid molecule described in connection with the second aspect of the invention. The second aspect defines a system. Where the product comprises a nucleic acid molecule described in connection with the second aspect, only the nucleic acid molecule is necessarily incorporated into the product. The product does not need to comprise the system of the second aspect, and / or other non-nucleic acid components of the system of the second aspect. The first and / or second nucleic acid molecule may be a guide nucleic acid molecule described herein. In the context of products and systems of the invention, the term “configured to target” a given transcription factor typically means that the product or system is purposively designed to target that transcription factor. For example, a system that is configured to target a transcription factor may comprise a guide RNAthat is complementary or reverse complementary to a region of the transcription factor gene. It cannot be excluded that a product or system that is “configured to target” a given transcription factor has an indirect effect on expression of another transcription factor (e.g. Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, orAtohl). However, such a product or system is not for directly increasing the protein expression of another transcription factor (e.g. Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, orAtohl). Alternatively, in some embodiments, a product or system that is “configured to target” a given transcription factor may not have an indirect effect on the expression of another transcription factor (e.g. Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, orAtohl).

[1304] The first nucleic acid molecule may be any guide nucleic acid sequence described herein. The first nucleic acid molecule may be any guide nucleic acid molecule described herein.

[1305] The second nucleic acid molecule may be any guide nucleic acid sequence described herein. The second nucleic acid molecule may be any guide nucleic acid molecule described herein.

[1306] The product may comprise two or more nucleic acid molecules that between them target for upregulation any two or more transcription factors, or functional variants thereof, described elsewhere herein. For example, the transcription factors may comprise:

[1307] (a) Pou4f3 and Gfi1 ;

[1308] (b) Gfi1 and Lhx3;

[1309] (c) Gfi1 and Six2;

[1310] (d) Lhx3 and Six2;

[1311] (e) Isl1 and Kcnip3;

[1312] (f) Pknox2 and Kcnip3;

[1313] (g) Pou4f3, Gfi1 and Lhx3;

[1314] (h) Pou4f3, Gfi1 and Six2;

[1315] (I) Pou4f3, Gfi1 and Kcnip3;

[1316] 0) Pou4f3, Gfi1 , Lhx3 and Six2;

[1317] (k) Pou4f3, Gfi1 , Isl1 and Kcnip3; or

[1318] (l) Pou4f3, Gfi1 , Pknox2 and Kcnip3.

[1319] It is not excluded that the product, such as the first or second nucleic acid molecule, may target for upregulation one or more further transcription factor not selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3. However, the product, such as the first or second nucleic acid molecule, may not target for upregulation Atohl or a functional variant thereof.

[1320] Embodiments of the product of the sixth aspect may correspond to embodiments of the product of the fifth aspect, wherein any reference to what is encoded by the nucleic acid molecules of the fifth aspect is replaced with a reference to what is targeted for upregulation by the nucleic acid molecules of the sixth aspect. The product of the sixth aspect may further comprise a third nucleic acid molecule that targets for upregulation anything said to be expressed by the third nucleic acid molecule of the fifth aspect. The product of the sixth aspect may further comprise a fourth nucleic acid molecule that targets for upregulation anything said to be expressed by the third nucleic acid molecule of the fifth aspect.

[1321] The product may further comprise any gene activating protein or nucleic acid molecule encoding a gene activating protein described in connection with the second aspect of the invention. The second aspect defines a system. Where the product comprises a gene activating protein or nucleic acid molecule encoding a gene activating protein described in connection with the second aspect, only the gene activating protein or nucleic acid molecule encoding a gene activating protein is necessarily incorporated into the product. The product does not need to comprise the system of the second aspect, and / or other non-gene activating protein or nucleic acid molecule encoding a gene activating protein components of the system of the second aspect. The gene activating protein may be encoded by the first and / or second nucleic acid molecule. The gene activating protein may be encoded by a third and / or fourth nucleic acid molecule.

[1322] According to a seventh aspect, the invention provides a kit for introducing and / or increasing the protein expression of at least two transcription factors, or functional variants thereof, in a source cell, wherein the at least two transcription factors are selected from the group consisting of Pou4f3, Gfi1 , Lhx3, Isl1 , Six2, Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

[1323] The kit may optionally further comprise instructions for introducing and / or increasing the protein expression of at least two transcription factors, or functional variants thereof, in a source cell.

[1324] The term “introducing” as used herein, refers to the introduction of an exogenous transcription factor. The term "exogenous," when used in relation to a protein, gene, nucleic acid, or polynucleotide in a cell or organism refers to a protein, gene, nucleic acid, or polynucleotide that has been introduced into the cell or organism by artificial or natural means; or in relation to a cell, refers to a cell that was isolated and subsequently introduced to other cells or to an organism by artificial or natural means. An exogenous nucleic acid may be from a different organism or cell, or it may be one or more additional copies of a nucleic acid that occurs naturally within the organism or cell. An exogenous cell may be from a different organism, or it may be from the same organism. By way of a non-limiting example, an exogenous nucleic acid is one that is in a chromosomal location different from that of natural cells or is otherwise flanked by a different nucleic acid sequence than that found in nature. An exogenous nucleic acid may also be extra- chromosomal, such as an episomal vector. An exogenous transcription factor may therefore be from a different organism or cell, or it may be one or more additional copies of a transcription factor that occurs naturally within the organism or cell.

[1325] The term “increasing” or “increase” as used herein, means to induce or increase or activate a level, activity or function or expression of a transcription factor in the source cell. The activity may be induced or increased or activated by 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more compared to a comparator value (i.e. a control). For example, a control may a source cell into which no expression cassettes encoding the nucleic ac...

Claims

Claims1 . A nucleic acid molecule encoding at least two transcription factors, or functional variants thereof, selected from the group consisting of Gfi1 , Pou4f3, Lhx3, Six2, Isl1 ,Pknox2 and Kcnip3, wherein the nucleic acid molecule does not encode Atohl .

2. The nucleic acid molecule according to claim 1 wherein the transcription factors comprise:(a) Pou4f3 and Gfi1 ;(b) Gfi1 and Lhx3;(c) Gfi1 and Six2;(d) Pou4f3, Gfi1 and Lhx3;(e) Pou4f3, Gfi1 and Six2;(f) Pou4f3, Gfi1 , Lhx3 and Six2;(g) Lhx3 and Six2;(h) Isl1 and Kcnip3;(I) Pknox2 and Kcnip3;Pou4f3, Gfi1 and Kcnip3;(j) Pou4f3, Gfi1 , Isl1 and Kcnip3; or(k) Pou4f3, Gfi1 , Pknox2 and Kcnip3.

3. The nucleic acid molecule according to any preceding claim wherein the nucleic acid molecule encodes Pou4f3 and Gfl 1 , or functional variants thereof.

4. The nucleic acid molecule according to any preceding claim wherein the nucleic acid molecule encodes Pou4f3 and Gfl1 .

5. The nucleic acid molecule according to claim 1 wherein the nucleic acid molecule encodes Gfl1 and Lhx3, or functional variants thereof.

6. The nucleic acid molecule according to claim 1 wherein the nucleic acid molecule encodes Gfl1 and Six2, or functional variants thereof.

7. The nucleic acid molecule according to any one of claims 1 to 5 wherein the nucleic acid molecule encodes Pou4f3, Gfi1 and Lhx3, or functional variants thereof.

8. The nucleic acid molecule according to any one of claims 1 to 4 or 6 wherein the nucleic acid molecule encodes Pou4f3, Gfi1 and Six2, or functional variants thereof.

9. The nucleic acid molecule according to any preceding claim wherein the nucleic acid molecule encodes Pou4f3, Gfl 1 , Lhx3 and Six2, or functional variants thereof.

10. The nucleic acid molecule according to any one of claims 1 to 4 wherein the nucleic acid molecule encodes Pou4f3, Gfi1 and Kcnip3, or functional variants thereof.11 . The nucleic acid molecule according to any one of claims 1 to 4 or 7 to 10 wherein the nucleic acid sequence encoding Gfi1 is 5’ relative to the nucleic acid sequence encoding Pou4f3.

12. The nucleic acid molecule according to claim 1 wherein the nucleic acid molecule encodes Lhx3 and Six2, or functional variants thereof.

13. The nucleic acid molecule according to any one of claims 1 , 9 or 12 wherein the nucleic acid sequence encoding Lhx3 is 5’ relative to the nucleic acid sequence encoding Six2.

14. The nucleic acid molecule according to claim 1 wherein the nucleic acid molecule encodes Isl1 and Kcnip3, or functional variants thereof.

15. The nucleic acid molecule according to any one of claims 1 or 14 wherein the nucleic acid sequence encoding Isl1 is 5’ relative to the nucleic acid sequence encoding Kcnip3.

16. The nucleic acid molecule according to claim 1 wherein the nucleic acid molecule encodes Pknox2 and Kcnip3, or functional variants thereof.

17. The nucleic acid molecule according to any one of claims 1 or 16 wherein the nucleic acid sequence encoding Pknox2 is 5’ relative to the nucleic acid sequence encoding Kcnip3.

18. The nucleic acid molecule according to any preceding claim further comprising a linker sequence separating sequences encoding transcription factors, optionally wherein the linker sequence encodes a 2A family peptide or comprises an IRES, optionally wherein the 2A family peptide is selected from the group consisting of P2A, T2A, E2A and F2A.

19. The nucleic acid molecule according to any preceding claim wherein the nucleic acid molecule is for expression of the at least two transcription factors in a source cell, optionally wherein a source cell is a cochlear cell, optionally an inner ear non-sensory cell, optionally wherein the inner ear non-sensory cell is selected from the group consisting of a Dieters’ cell, a pillar cell, a Kolliker’s organ cell, a lesser epithelial ridge cell, an inner phalangeal cell, an inner border cell, a greater epithelial ridge cell, an inner sulcus cell or an outer sulcus cell.

20. The nucleic acid molecule according to any preceding claim wherein the nucleic acid molecule is for expression of the at least two transcription factors in a Dieters’ cell, a pillar cell or a Kolliker’s organ cell.21 . The nucleic acid molecule according to any preceding claim comprising a promoter operably linked to the sequences encoding the at least two transcription factors, wherein the promoter is for expression of the at least two transcription factors in a source cell, optionally wherein a source cell is a cochlear cell, optionally an inner ear non-sensory cell, optionally wherein the inner ear non-sensory cell is selected from the group consisting of a Dieters’ cell, a pillar cell, a Kolliker’s organ cell, a lesserepithelial ridge cell, an inner phalangeal cell, an inner border cell, a greater epithelial ridge cell, an inner sulcus cell or an outer sulcus cell.

22. The nucleic acid molecule according to any preceding claim comprising a promoter operably linked to the sequences encoding the at least two transcription factors, wherein the promoter is for expression of the at least two transcription factors in a Dieters’ cell, a pillar cell or a Kolliker’s organ cell.

23. The nucleic acid molecule according to any preceding claim wherein the promoter comprises a CMV enhancer region, or a functional variant thereof, optionally wherein the promoter is selected from the group consisting of CAG, CBA, CBh, sCAG, CMV1 and CMV2.

24. The nucleic acid molecule according to any preceding claim wherein the promoter comprises a chicken p actin promoter region, or a functional variant thereof, optionally wherein the promoter is selected from the group consisting of CAG, CBA, CBh and sCAG.

25. The nucleic acid molecule according to any preceding claim wherein the promoter comprises a CMV promoter region, or a functional variant thereof, optionally wherein the promoter is selected from the group consisting of CMV1 and CMV2.

26. The nucleic acid molecule according to any preceding claim wherein the promoter comprises CAG, CBA, CBh, sCAG or CMV, or a functional variant thereof.

27. The nucleic acid molecule according to any preceding claim wherein the promoter comprises CAG.

28. A vector comprising the nucleic acid molecule according to any one of claims 1 to 27.

29. A vector according to claim 28, wherein the vector is a viral vector, optionally wherein the viral vector is selected from the group consisting of an adeno-associated virus (AAV) vector, a lentiviral vector, a Sendai vector, a Herpes simplex virus (HSV) vector, an Adenoviral vector, an episomal vector and a retroviral vector.

30. A vector according to any one of claims 28 to 29, wherein the vector comprises a capsid for transduction of cochlear cells, optionally wherein the vector comprises a capsid for transduction of a cell type selected from the group consisting of a Dieters’ cell, a pillar cell, a Kolliker’s organ cell, a lesser epithelial ridge cell, an inner phalangeal cell, an inner border cell, a greater epithelial ridge cell, inner sulcus cells and outer sulcus cells.31 . A vector according to any one of claims 28 to 30, wherein the vector comprises a capsid selected from the group consisting of AAV9, AAVShHI 0, AAV1 , AAV2, AAV5, AAV7, AAV8, AAV2 / 1 , AAV2 / 2, AAV2 / 5, AAV2 / 7, AAV2 / 8, AAV2 / 9, AAV-DJ, AAV-ie, AAV-2.7m8, Anc80L65 and AAV-KP1 .

32. A vector according to any one of claims 28 to 31 , wherein the vector comprises an AAV-DJ capsid.

33. A vector according to claim 28, wherein the vector is a non-viral vector, optionally wherein the non- viral vector is selected from the group consisting of a liposome, a nanoparticle, an exosome, a viruslike particle (VLP), a lipid nanoparticle (LNP), naked DNA, a plasmid, a transposon, a repRNA vector, mRNA and stabilised RNA.

34. A composition comprising the nucleic acid molecule according to any one of claims 1 to 27, or the vector according to any one of claims 28 to 33, and a pharmaceutically acceptable carrier.

35. A product comprising(a) a first nucleic acid molecule, encoding at least one transcription factor, or a functional variant thereof, selected from the group consisting of Gfi 1 , Pou4f3, Lhx3, Six2, Isl 1 , Pknox2 and Kcnip3, and(b) a second nucleic acid molecule, encoding at least one transcription factor, or a functional variant thereof, selected from the group consisting of Gfi1 , Pou4f3, Lhx3, Six2, Isl1 , Pknox2 and Kcnip3;(c) wherein the first nucleic acid molecule and the second nucleic acid molecule each encode different transcription factors,(d) and wherein the product does not comprise a nucleic acid molecule encoding Atohl ; for use in the treatment of hearing loss, wherein the product is a combined preparation for simultaneous, separate or sequential administration.

36. The product according to claim 35 wherein the first and / or second nucleic acid molecule is a nucleic acid molecule according to any one of claims 1 to 27.

37. The product according to any one of claims 35 to 36 wherein the first and second nucleic acid molecules together encode transcription factors or functional variants thereof comprising:(a) Pou4f3 and Gfi1 ;(b) Gfi1 and Lhx3;(c) Gfi1 and Six2;(d) Pou4f3, Gfi1 and Lhx3;(e) Pou4f3, Gfi1 and Six2;(f) Pou4f3, Gfi1 , Lhx3 and Six2;(g) Lhx3 and Six2;(h) Isl1 and Kcnip3;(I) Pknox2 and Kcnip3;(j) Pou4f3, Gfi1 and Kcnip3;(k) Pou4f3, Gfi1 , Isl1 and Kcnip3; or(l) Pou4f3, Gfi1 , Pknox2 and Kcnip3.

38. The product according to any one of claims 35 to 37 wherein the first nucleic acid molecule encodes Pou4f3 or a functional variant thereof, and the second nucleic acid molecule encodes Gfi1 , or a functional variant thereof.

39. The product according to any one of claims 35 to 37 wherein the first nucleic acid molecule encodes Pou4f3 and Gfl 1 , or functional variants thereof.

40. The product according to any one of claims 35 to 37 wherein the first nucleic acid molecule encodes Gfl 1 or a functional variant thereof, and the second nucleic acid molecule encodes Lhx3, or a functional variant thereof.41 . The product according to any one of claims 35 to 37 wherein the first nucleic acid molecule encodes Gfl1 and Lhx3, or functional variants thereof.

42. The product according to any one of claims 35 to 37 wherein the first nucleic acid molecule encodes Gfl 1 or a functional variant thereof, and the second nucleic acid molecule encodes Six2, or a functional variant thereof.

43. The product according to any one of claims 35 to 37 wherein the first nucleic acid molecule encodes Gfl1 and Six2, or functional variants thereof.

44. The product according to any one of claims 35 to 37 wherein the first nucleic acid molecule encodes Pou4f3 and Gfl 1 , or functional variants thereof, and the second nucleic acid molecule encodes at least two transcription factors, or functional variants thereof, selected from the group consisting of Lhx3, Six2, Isl1 , Pknox2 and Kcnip3.

45. The product according to any one of claims 35 to 37 or 44 wherein the first nucleic acid molecule encodes Pou4f3 and Gfl1 , or functional variants thereof, and the second nucleic acid molecule encodes Lhx3 and Six2, or functional variants thereof.

46. The product according to any one of claims 35 to 37 or 44 wherein the first nucleic acid molecule encodes Pou4f3 and Gfl1 , or functional variants thereof, and the second nucleic acid molecule encodes Isl1 and Kcnip3, or functional variants thereof.

47. The product according to any one of claims 35 to 37 or 44 wherein the first nucleic acid molecule encodes Pou4f3 and Gfl1 , or functional variants thereof, and the second nucleic acid molecule encodes Pknox2 and Kcnip3, or functional variants thereof.

48. A kit for introducing and / or increasing the protein expression of at least two transcription factors, or functional variants thereof, in a source cell, wherein the kit comprises at least two transcription factors which are selected from the group consisting of Gfi1 , Pou4f3, Lhx3, Six2, Isl1 , Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

49. The kit according to claim 48 wherein the transcription factors for introducing and / or increasing comprise:(a) Pou4f3 and Gfi1 ;(b) Gfi1 and Lhx3;(c) Gfi1 and Six2;(d) Pou4f3, Gfi1 and Lhx3;(e) Pou4f3, Gfi1 and Six2;(f) Pou4f3, Gfi1 , Lhx3 and Six2;(g) Lhx3 and Six2;(h) Isl1 and Kcnip3;(i) Pknox2 and Kcnip3;Pou4f3, Gfi1 and Kcnip3;(j) Pou4f3, Gfi1 , Isl1 and Kcnip3; or(k) Pou4f3, Gfi1 , Pknox2 and Kcnip3.

50. A kit according to any one of claims 48 to 49 for the introduction of transcription factors, the kit comprising a nucleic acid molecule according to any one of claims 1 to 27, a vector according any one of claims 28 to 33, a composition according to claim 34 or a product according to any one of claims 35 to 47.51 . A product or kit according to any one of claims 35 to 50, further comprising instructions for use.

52. A method of converting a source cell to a target cell by introducing and / or increasing the protein expression of at least two transcription factors, or functional variants thereof, into the source cell, thereby converting the source cell into the target cell, wherein the at least two transcription factors are selected from the group consisting of Gfi 1 , Pou4f3, Lhx3, Six2, Isl 1 , Pknox2 and Kcnip3, wherein the at least two transcription factors do not comprise Atohl .

53. The method according to claim 52 wherein the transcription factors introduced and / or increased comprise:(a) Pou4f3 and Gfi1 ;(b) Gfi1 and Lhx3;(c) Gfi1 and Six2;(d) Pou4f3, Gfi1 and Lhx3;(e) Pou4f3, Gfi1 and Six2;(f) Pou4f3, Gfi1 , Lhx3 and Six2;(g) Lhx3 and Six2;(h) Isl1 and Kcnip3;(l) Pknox2 and Kcnip3;Pou4f3, Gfi1 and Kcnip3;(j) Pou4f3, Gfi1 , Isl1 and Kcnip3; or(k) Pou4f3, Gfi1 , Pknox2 and Kcnip3.

54. The method according to any one of claims 52 to 53 wherein the method is for introducing the transcription factors and the transcription factors may be introduced via a nucleic acid molecule according to any one of claims 1 to 27 , a vector according to any one of claims 28 to 33, a compositionaccording to claim 34, a product according to any one of claims 35 to 47 or a kit according to any one of claims 48 to 51 .

55. The method according to any one of claims 52 to 54 wherein the method is an in vitro method comprising comprise culturing under suitable conditions for a time period suitable for conversion of the source cell to the target cell, optionally culturing under suitable conditions for at least 7 days.

56. A cell produced by the method of any one of claims 52 to 55.

57. A nucleic acid molecule according to any one of claims 1 to 27, a vector according to any one of claims 28 to 33, a composition according to claim 34, a kit according to any one of claims 48 to 51 , or a cell according to claim 56 in the treatment of hearing loss.

58. A method of treating hearing loss in a subject in need thereof comprising administering to the subject a therapeutically effective amount of a nucleic acid molecule according to any one of claims 1 to 27, a vector according to any one of claims 28 to 33, a composition according to claim 34, a product according to any one of claims 35 to 47, a kit according to any one of claims 48 to 51 , or a cell according to claim 56.

59. A nucleic acid molecule, vector, composition, product, kit, a method, cell, substance or composition for use or a method of treatment according to any preceding claim, wherein a source cell is a cochlear cell, optionally an inner ear non-sensory cell, optionally wherein the inner ear non-sensory cell is selected from the group consisting of a Dieters’ cell, a pillar cell, a Kolliker’s organ cell, a lesser epithelial ridge cell, an inner phalangeal cell, an inner border cell, a greater epithelial ridge cell, an inner sulcus cell or an outer sulcus cell.

60. A nucleic acid molecule, vector, composition, product, kit, a method, cell, substance or composition for use or a method of treatment according to any preceding claim, wherein a source cell is a Dieters’ cell, a pillar cell or a Kolliker’s organ cell.

61. A nucleic acid molecule, vector, composition, product, kit, a method, cell, substance or composition for use or a method of treatment according to any preceding claim, wherein a target cell is an inner hair cell, inner hair-like cell, outer hair cell or an outer hair-like cell.

62. A nucleic acid molecule, vector, composition, product, kit, a method, cell, substance or composition for use or a method of treatment according to any preceding claim, wherein a cell or a cell population in which the transcription factors are introduced and / or increased:(a) upregulates one or more cochlear hair cell markers;(b) downregulates one or more cell markers of a source cell;(c) undergoes one or more morphological change indicative of conversion from a source cell to a cochlear hair cell; and / or(d) is annotated as a cochlear hair cell by inspecting the expression of marker genes, for example by annotation using SingleR, such as version 2.0.

063. A nucleic acid molecule, vector, composition, product, kit, a method, cell, substance or composition for use or a method of treatment according to claim 62 wherein the cell or cell population upregulates:(a) one or more inner hair cell markers, optionally selected from the group consisting of Myo7a, Slc26a5, Ocm, Calbl , Myo6 and Espn; and / or(b) one or more outer hair cell markers, optionally selected from the group consisting of Myo7a, Vglut3, Calbl and Otof.

64. A nucleic acid molecule, vector, composition, product, kit, a method, cell, substance or composition for use or a method of treatment according to claim 62 or claim 63 wherein the cell or cell population down reg ulates:(a) one or more Dieters’ cell markers, optionally selected from the group consisting of Sox2, Lgr5, Mansc4, Lfng and Hes5;(b) one or more pillar cell markers, optionally selected from the group consisting of Sox2, Npy, Cep41 and Emidi ; and / or(c) one or more Kolliker’s organ markers, optionally selected from the group consisting of Sox2, Gjb6, Epyc, Clu and Shisal2b.

65. A product according to any one of claims 35 to 47, a nucleic acid molecule, vector, composition, product, kit, a method or cell for use according to any one of claims 59 to 64, or a method of treatment according to any one of claims 58 to 64, wherein the hearing loss is sensorineural hearing loss, optionally wherein the sensorineural hearing loss is one or more of:(a) severe to profound sensorineural hearing loss;(b) noise induced sensorineural hearing loss;(c) age induced sensorineural hearing loss; and / or(d) ototoxic drug induced sensorineural hearing loss, optionally wherein the ototoxic drug is an antibiotic, optionally wherein the antibiotic is an aminoglycoside.

66. A product according to any one of claims 35 to 47 or 65, a nucleic acid molecule, vector, composition, product, kit, a method or cell for use according to any one of claims 59 to 65 , or a method of treatment according to any one of claims 58 to 65, wherein the administration is to one or more cochlea of the subject, optionally by round-window membrane injection, round-window membrane diffusion, cochleostomy or canalostomy.

67. A product according to any one of claims 35 to 47 or 65 to 66 , a nucleic acid molecule, vector, composition, product, kit, a method or cell for use according to any one of claims 59 to 66 , or a method of treatment according to any one of claims 58 to 66, wherein the hearing loss is in a subject who is a paediatric patient.

68. A product according to any one of claims 35 to 47 or 65 to 67, a nucleic acid molecule, vector, composition, product, kit, a method or cell for use according to any one of claims 59 to 67 , or a method of treatment according to any one of claims 58 to 67, wherein the administration does not comprise simultaneous, separate or sequential administration ofAtohl .

69. A product according to any one of claims 35 to 47 or 65 to 68, a nucleic acid molecule, vector, composition, product, kit, a method or cell for use according to any one of claims 59 to 68, or a method of treatment according to any one of claims 58 to 68, wherein the subject has not previously been treated by introducing and / or increasing the expression ofAtohl .

70. A nucleic acid molecule, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any preceding claim, wherein the nucleotide sequence encoding Pou4f3 or a functional variant thereof comprises a nucleic acid sequence encoding:(a) SEQ ID NO: 1 ,(b) SEQ ID NO: 2,(c) an amino acid sequence having at least 70% identify to SEQ ID NO: 1 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 1 , or(d) an amino acid sequence having at least 70% identify to SEQ ID NO: 2 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 2.71 . A nucleic acid molecule, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any preceding claim, wherein the nucleotide sequence encoding Pou4f3 or a functional variant thereof comprises:(a) SEQ ID NO: 3,(b) SEQ ID NO: 4,(c) SEQ ID NO: 5,(d) SEQ ID NO: 57, or(e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 3, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 1 , or(f) a nucleotide sequence having at least 60% identity to SEQ ID NO: 4, SEQ ID NO: 5 or SEQ ID NO: 57, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 2.

72. A nucleic acid molecule, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any preceding claim, wherein the nucleotide sequence encoding Gfi1 or a functional variant thereof comprises a nucleic acid sequence encoding:(a) SEQ ID NO: 6,(b) SEQ ID NO: 7,(c) an amino acid sequence having at least 70% identify to SEQ ID NO: 6 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 6, or(d) an amino acid sequence having at least 70% identify to SEQ ID NO: 7 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 7.

73. A nucleic acid molecule, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any preceding claim, wherein the nucleotide sequence encoding Gfi 1 or a functional variant thereof comprises:(a) SEQ ID NO: 8,(b) SEQ ID NO: 9,(c) SEQ ID NO: 10,(d) SEQ ID NO: 58, or(e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 8, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 6, or(f) a nucleotide sequence having at least 60% identity to SEQ ID NO: 9, SEQ ID NO: 10 or SEQ ID NO: 58, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 7.

74. A nucleic acid molecule, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any preceding claim, wherein the nucleotide sequence encoding Lhx3 or a functional variant thereof comprises a nucleic acid sequence encoding:(a) SEQ ID NO: 11 ,(b) SEQ ID NO: 12,(c) an amino acid sequence having at least 70% identify to SEQ ID NO: 11 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 11 , or(d) an amino acid sequence having at least 70% identify to SEQ ID NO: 12 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 1275. A nucleic acid molecule, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any preceding claim, wherein the nucleotide sequence encoding Lhx3 or a functional variant thereof comprises:(a) SEQ ID NO: 13,(b) SEQ ID NO: 14,(c) SEQ ID NO: 15,(d) SEQ ID NO: 59, or(e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 13, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 11 , or(f) a nucleotide sequence having at least 60% identity to SEQ ID NO: 14, SEQ ID NO: 15 or SEQ ID NO: 59, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 12.

76. A nucleic acid molecule, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any preceding claim, wherein the nucleotide sequence encoding Six2 or a functional variant thereof comprises a nucleic acid sequence encoding:(a) SEQ ID NO: 21 ,(b) SEQ ID NO: 22,(c) an amino acid sequence having at least 70% identify to SEQ ID NO: 21 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 21 , or(d) an amino acid sequence having at least 70% identify to SEQ ID NO: 22 wherein the amino acid sequence defines a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 22.

77. A nucleic acid molecule, vector, composition, product, kit, method, cell, substance or composition for use or method of treatment according to any preceding claim, wherein the nucleotide sequence encoding Six2 or a functional variant thereof comprises:(a) SEQ ID NO: 23,(b) SEQ ID NO: 24,(c) SEQ ID NO: 25,(d) SEQ ID NO: 60, or(e) a nucleotide sequence having at least 60% identity to SEQ ID NO: 23, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 21 , or(f) a nucleotide sequence having at least 60% identity to SEQ ID NO: 24, SEQ ID NO: 25 or SEQ ID NO: 60, wherein the nucleotide sequence encodes a polypeptide which is a functional variant of a polypeptide defined by SEQ ID NO: 22.

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