Directional cDNA Library Construction via Modified Adaptor Cleavage
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Solution Overview
Problem
Current methods for directional cDNA sequencing using conventional duplex adaptors and blunt-end ligation fail to preserve strand information effectively, leading to loss of directional data, especially when using conventional duplex adaptors with universal sequencing sites.
Innovation Solution
A method involving the synthesis of first and second strand cDNA with incorporation of modified dNTPs, followed by end repair and ligation with adaptors where only one adaptor has the modified dNTP, allowing for selective cleavage and generation of directional cDNA libraries that retain strand orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional duplex adaptors with universal priming sites are used for blunt-end ligation, then library construction is simplified and cost-effective, but directional information (strand orientation) is lost
Solution Approach 1:
The patent applies local quality by making one strand of the adaptor asymmetric through incorporation of modified dNTPs (e.g., dUTP) only in the ligation strand. This creates a localized distinction between the two adaptor strands, allowing the ligation strand to be selectively degraded while preserving the non-ligation strand for sequencing. The modified dNTP incorporation is restricted to specific positions in the ligation strand, creating a targeted marker that enables directional information retention without compromising the overall simplicity of the library construction process.
Solution Approach 2:
The patent employs parameter changes by modifying the chemical composition of one strand of the adaptor through incorporation of modified dNTPs. This chemical modification creates a differential property between the ligation and non-ligation strands, enabling selective enzymatic degradation. The change in nucleotide composition (incorporation of dUTP vs. dTTP) serves as a marker that can be recognized by specific enzymes, thereby preserving directional information while maintaining compatibility with standard library construction workflows.
2Loss of information
If strand marking by bisulfite treatment is performed, then directional information can be obtained, but the process becomes labor intensive and requires complex alignment procedures
Solution Approach 1:
The patent extracts the directional information preservation function from the complex bisulfite treatment process by using a simpler adaptor-based marking system. Instead of chemically modifying the entire cDNA strand through bisulfite conversion, the method extracts only the necessary directional marker function by incorporating modified dNTPs specifically in the adaptor ligation strand. This extracted marking approach can be selectively degraded by enzymes like UNG or APE1, eliminating the need for labor-intensive bisulfite treatment and complex alignment procedures while still achieving directional information retention.
Solution Approach 2:
The patent uses a disposable marking system where the modified dNTP-containing ligation strand serves as a temporary marker that is intentionally degraded after serving its directional marking purpose. The modified strand acts as a sacrificial element that can be selectively removed by enzymatic treatment, leaving the unmodified non-ligation strand intact for sequencing. This disposable marking approach is simpler and more cost-effective than permanent chemical modifications like bisulfite treatment.
3Loss of information
If four-step process with cleavable nucleotides is used, then directional information can be preserved, but the process requires multiple steps including end repair, non-directional ligation, and selective hydrolysis
Solution Approach 1:
The patent merges multiple steps of the four-step process into a more streamlined workflow. By incorporating modified dNTPs directly during adaptor synthesis rather than requiring separate end repair and marking steps, the method combines adaptor preparation with strand marking. The blunt-end ligation step is maintained but becomes more meaningful as it now preserves directional information by default through the asymmetric adaptor design. The selective hydrolysis step is simplified by using enzymes that specifically recognize the modified dNTPs in the ligation strand, allowing simultaneous degradation of the marked strand and streamlining the overall process.
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 enables the construction of directional cDNA libraries that maintain strand information with high efficiency, allowing for accurate determination of strand orientation, as demonstrated by >97% retention of antisense strand sequences in coding exons.
Implementation Method 1
synthesizing first and second strand cDNA from template RNA, wherein either first strand cDNA or second strand cDNA synthesis comprises incorporating a modified dNTP
Implementation Method 2
selectively cleaving the first or the second strand cDNA and the adaptor that has the modified dNTP by a suitable cleavage agent
Implementation Method 3
ligating adaptors to the double-stranded cDNA, wherein only one of the adaptors has the modified dNTP incorporated into a ligation strand of the adaptor
Implementation Method 4
performing end repair on the double-stranded cDNA
Implementation Method 5
performing gap repair
Data Source
AI summary
The invention provides methods and compositions for directional nucleic acid amplification and sequencing. The invention further provides methods and compositions for the construction of directional eDNA libraries. The method may comprise: a) reverse transcribing a RNA sample to generate a first strand eDNA; b) generating a second strand eDNA from the rrrst strand eDNA, wherein at least one of the four dNTPs dATP, dCTP, dGTP or dTTP is replaced by a modified dNTP during second strand synthesis and incorporated into the second strand, thereby generating a double-stranded eDNA; c) performing end repair on the double-stranded eDNA; d) Iigating adaptors to the double-stranded eDIMA, wherein only one of the adaptors has the modified dNTP incorporated into a ligation strand of the adaptor; e) performing gap repair; and f) selectively cleaving the second strand and the ligation strand of the adaptor that has the modified dNTP by a suitable cleavage agent.