Hairpin DNA Sequencing for Methylation Mapping Without 4-Letter Code Loss
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Solution Overview
Problem
Current high-throughput techniques for identifying DNA methylation, such as Illumina sequencing, require complete conversion of cytosine to uracil, leading to loss of sequence information and the need for specialized technologies and reference genomes, and methods like Liang et al. (2021) fail to retain the 4-letter code across both DNA strands.
Innovation Solution
A method involving ligation of a hairpin adaptor to DNA, enzymatic generation of a free 3′ end, and extension with modified dCTP to create a deamination-resistant strand, allowing both strands to be read in paired-end sequencing without losing sequence information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complete conversion of cytosine to uracil is performed using chemical or enzymatic treatment, then methylation identification is achieved, but sequence information is lost and genome sequence complexity is reduced
Solution Approach 1:
The method separates the two DNA strands and applies different treatments to each strand. One strand undergoes complete deamination for methylation detection, while the other strand is protected and sequenced to recover sequence information. This segmentation allows both methylation identification and sequence information retention to be achieved simultaneously.
Solution Approach 2:
The patent introduces an intermediary protective mechanism using modified nucleotides (such as pyrrolo-dCTP or N4-dmCTP) that protect cytosines on one strand from deamination. This intermediary protection allows the sequence information to be preserved while the complementary strand undergoes complete deamination for methylation analysis.
2Quantity of substance
If both DNA strands are subjected to bisulfite conversion, then methylation information is obtained from both strands, but the 4-letter code is lost and sequence information cannot be retrieved
Solution Approach 1:
The method divides the treatment approach by strand: one strand receives full deamination treatment for methylation detection, while the other strand is protected with modified nucleotides and subjected to limited or no deamination. This segmentation ensures that methylation information is captured from both strands while sequence information is preserved on at least one strand.
Solution Approach 2:
Different quality states are applied to different strands: one strand is fully deaminated to maximize methylation detection sensitivity, while the other strand maintains its original quality with protected cytosines to preserve sequence information. This local differentiation of treatment quality resolves the contradiction between maximizing methylation information and preserving sequence code.
3Measurement precision
If specialized technologies and reference genomes are used for methylation identification, then accurate methylation profiles are obtained, but additional experiments are required and process complexity increases
Solution Approach 1:
The method merges methylation detection and sequence information retrieval into a single integrated workflow. By protecting one strand during deamination and sequencing both strands, the technique combines what were previously separate experiments (methylation analysis and sequence determination) into one unified process, reducing overall complexity.
Solution Approach 2:
The patent creates a multi-functional method that simultaneously performs methylation detection, sequence determination, and variant identification in a single experimental workflow. This universal approach eliminates the need for separate specialized experiments and reference genome requirements, simplifying the overall process while maintaining accuracy.
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
Enables simultaneous identification of sequence variations and methylation patterns at single-molecule resolution, retaining the 4-letter code and enabling enrichment using conventional probes.
Implementation Method 1
a hairpin adaptor followed by bisulfite treatment
Implementation Method 2
converting cytosine to uracil, leaving 5′methylcytosine (5mC) intact. This conversion is done using chemical treatment (bisulfite)
Implementation Method 3
extending the free 3′ end in a dCTP-free reaction mix that comprises a strand-displacing or nick-translating polymerase, dGTP, dATP, dTTP and modified dCTP to generate a hairpin product that has an original strand and a neosynthesized strand that contains modified Cs
Data Source
AI summary
Provided herein is a method for generating a strand of DNA. In some embodiments, this method may comprise: (a) ligating a hairpin adaptor to a double-stranded fragment of DNA to produce a ligation product; (b) enzymatically generating a free 3′ end in a double-stranded region of the hairpin adaptor in the ligation product; and (c) extending the free 3′ end in a dCTP-free reaction mix that comprises a strand-displacing or nick-translating polymerase, dGTP, dATP, dTTP and modified dCTP to generate a hairpin product that has an original strand and a neosynthesized strand that contains modified Cs.