Methylated CpG Island Enrichment via Bisulfite Conversion
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Solution Overview
Problem
Current techniques for detecting methylated CpG islands in genomes are inefficient and costly, particularly when using high-throughput sequencing, as they often require complex library establishment processes and cannot distinguish between methylated and unmethylated CpG islands, limiting their applicability to large sample sets.
Innovation Solution
A method involving high-CpG-density oligonucleotide primers for enriching and amplifying methylated CpG islands from bisulfite-converted DNA samples, using a three-step PCR reaction to anchor adapter sequences for subsequent high-throughput sequencing, allowing for efficient and cost-effective detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If reduced representation bisulfite sequencing is used to enrich CpG islands, then sequencing cost is reduced, but the library establishment process becomes complex and time-consuming (5-6 days)
Solution Approach 1:
The patent performs bisulfite conversion of genomic DNA before enrichment, which permanently modifies unmethylated cytosines to uracils. This preliminary chemical transformation simplifies subsequent enrichment steps because only methylated CpG regions remain as templates for primer binding and amplification, eliminating the need for complex gel purification and size selection required in traditional reduced representation bisulfite sequencing
Solution Approach 2:
The patent uses high-CpG-density primers that specifically target methylated CpG islands through PCR amplification after bisulfite conversion. By changing the enrichment mechanism from physical separation (gel purification) to specific biochemical amplification (PCR with targeted primers), the method reduces both time and operational complexity while maintaining cost-effectiveness
2Quantity of substance
If traditional enrichment methods are used, then CpG islands can be enriched, but the process cannot distinguish between methylated and unmethylated CpG islands, increasing sequencing cost
Solution Approach 1:
The patent converts the potential harm of bisulfite conversion (which destroys unmethylated cytosines) into a beneficial enrichment mechanism. By treating DNA with bisulfite before enrichment, unmethylated regions are permanently altered and cannot serve as templates for primer binding, while methylated CpG regions remain intact and are selectively amplified. This transforms a chemical modification that could be seen as damaging into a powerful selective enrichment tool
Solution Approach 2:
The patent introduces high-CpG-density primers as intermediaries that specifically recognize and bind to methylated CpG sequences after bisulfite conversion. These primers act as mediators between the bisulfite-converted DNA and the PCR amplification process, enabling selective enrichment of methylated regions without requiring complex antibody-based or protein-based enrichment methods
3Measurement precision
If whole-genome bisulfite sequencing is used, then single-base-pair resolution is achieved, but the cost is very high, hampering application to large numbers of samples
Solution Approach 1:
The patent extracts and selectively amplifies only the methylated CpG island regions from the genome after bisulfite conversion, rather than sequencing the entire genome. By taking out and enriching only the relevant methylated sequences using high-CpG-density primers, the method achieves the same measurement precision for CpG islands at a fraction of the cost of whole-genome sequencing
Solution Approach 2:
The patent performs partial sequencing by focusing only on methylated CpG islands rather than the entire genome. The bisulfite conversion is applied to whole genomic DNA, but subsequent enrichment and sequencing are limited to the subset of methylated CpG regions, providing sufficient precision for CpG island analysis while dramatically reducing sequencing depth and cost requirements
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 significantly enhances the enrichment of methylated CpG islands, reducing the time and cost associated with library establishment and achieving high-resolution, efficient detection, with the ability to selectively amplify methylated regions while minimizing non-specific amplification.
Implementation Method 1
The bisulfite sequencing is based on the fact that sodium bisulfite treatment converts unmethylated cytosines (C) to uracils (U) whereas methylated cytosines (5mC) are not affected
Implementation Method 2
followed by end-repair, A tailing, adapter ligation, size selection and PCR amplification to obtain the library
Data Source
AI summary
A high-throughput sequencing method for detecting methylated CpG islands includes: processing a DNA sample by using a modifier, and converting cytosine in the DNA sample into uracil, and keeping 5′methylcytosine unchanged; amplifying the obtained segment by using a primer A and DNA polymerase, to obtain a segment having one end being capable of anchoring a junction primer C; amplifying the obtained segment by using a primer B and DNA polymerase, to obtain a segment gathering methylated CpG islands and having two ends being capable of separately anchoring junction primers C and D; amplifying the obtained segment at a PCR exponent by using the junction primers C and D and the DNA polymerase, to obtain the amplified product; and separating and purifying the amplified product, to form a high-throughput sequencing library and perform computer sequencing, and data analysis.