Scarless Targeting Vector Construction via BHR and In Vitro Assembly
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Solution Overview
Problem
Current methods for creating transgenic animal lines often result in scars from restriction sites or manipulations that can negatively impact gene expression, especially when targeting large regions of the mammalian genome, leading to unintended effects on gene regulation and faithful expression of humanized alleles.
Innovation Solution
The development of methods for scarless introduction of targeted genetic modifications into preexisting targeting vectors using bacterial homologous recombination and in vitro assembly, which involve performing bacterial homologous recombination between the targeting vector and a modification cassette, selecting cells with the modified vector, cleaving specific sites to remove selection cassettes, and assembling the vector in an intramolecular or intermolecular reaction to generate a scarless modification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional restriction site-based methods are used for DNA construction, then the targeting vector can be assembled, but scars from restriction sites are introduced that negatively impact gene expression
Solution Approach 1:
The patent removes harmful restriction sites and selection cassettes from the final targeting vector through sequential cleavage steps. The selection cassette is excised using specific nucleases that recognize and cut at defined sites, eliminating the scar-forming elements while preserving the desired genetic modification.
Solution Approach 2:
The patent introduces placeholder sequences and protective elements during the initial assembly phase that facilitate subsequent scarless editing. These preliminary elements are designed to be temporarily present during construction but are removed in later steps, enabling the final vector to be free of scars.
2Adaptability or versatility
If multiple modifications are added to create complex animal models, then the model complexity increases, but more scars and selection cassettes are introduced that increase the likelihood of expression alteration
Solution Approach 1:
The patent divides the construction process into discrete modular steps, each adding a specific modification while using standardized assembly protocols. This segmentation allows multiple changes to be introduced systematically, with each step followed by scar removal, preventing cumulative scar burden.
Solution Approach 2:
The patent employs selection cassettes that are intentionally introduced for their utility during construction and selection, then systematically discarded in subsequent steps. The cassettes serve their purpose during cloning and verification, then are removed to leave a clean final construct without scar sequences.
3Productivity
If selection cassettes are included in the targeting vector, then selection of embryonic stem cell clones is enabled, but the cassettes themselves constitute scars that may affect gene regulation
Solution Approach 1:
The patent implements a periodic workflow where selection cassettes are introduced, used for their intended purpose, then removed in scheduled steps. The cassette is present during critical selection phases, then systematically excised using nuclease-based methods to leave no residual scar.
Solution Approach 2:
The patent uses selection cassettes as temporary intermediary elements that facilitate the construction and selection process but are not part of the final product. These intermediaries perform their mediating function during cloning and selection, then are eliminated to reveal the clean final construct.
4Manufacturing precision
If homologous recombination is performed with modification cassettes containing selection cassettes, then the genetic modification is introduced, but the selection cassette must be removed to achieve scarless modification
Solution Approach 1:
The patent replaces traditional mechanical restriction enzyme-based excision with nuclease-based site-specific cleavage. This substitution allows for more precise and flexible removal of selection cassettes, enabling scarless editing even in contexts where traditional restriction sites are unavailable or would create unwanted scars.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for efficient and scarless integration of targeted genetic modifications, minimizing the introduction of undesired sequences and maintaining faithful gene expression, even in complex animal models with multiple modifications.
Implementation Method 1
performing bacterial homologous recombination between the preexisting targeting vector and a modification cassette in a population of bacterial cells
Implementation Method 2
cleaving the first target site in the modified targeting vector with the first nuclease agent and cleaving the second target site in the modified targeting vector with the second nuclease agent
Implementation Method 3
treating the modified targeting vector with an exonuclease to expose complementary sequences
Implementation Method 4
annealing the exposed complementary sequences
Implementation Method 5
extending the 3' ends of the annealed complementary sequences
Implementation Method 6
ligating the annealed complementary sequences
Data Source
AI summary
Methods for introducing a scarless targeted genetic modification into a preexisting targeting vector are provided. The methods can use combinations of bacterial homologous recombination (BHR) and in vitro assembly to introduce such targeted genetic modifications into a preexisting targeting vector in a scarless manner.