Cell-Free Methylated DNA Capture for Low-Input Sequencing
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Solution Overview
Problem
Existing methods for genome-wide DNA methylation mapping of cell-free DNA (cfDNA) are challenging due to low DNA amounts and fragmentation, making techniques like MeDIP-seq and RRBS impractical, and the low abundance of methylated DNA limits sensitivity in detecting cancer-specific alterations.
Innovation Solution
A method called cfMeDIP-seq is developed, which involves adding filler DNA to samples, denaturing them, and using a binder selective for methylated polynucleotides to capture cell-free methylated DNA, enabling sequencing even with low input amounts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional MeDIP-seq or RRBS methods are used for genome-wide DNA methylation mapping, then comprehensive methylation profiling can be achieved, but the methods become impractical due to low DNA amounts and fragmentation in cell-free DNA samples
Solution Approach 1:
The patent modifies the MeDIP-seq protocol by changing key parameters: using optimized antibody incubation conditions, adjusting sonication parameters for DNA fragmentation, and modifying purification steps to work efficiently with low-input cfDNA samples. These parameter changes enable traditional MeDIP-seq to become practical for cfDNA analysis while maintaining methylation mapping accuracy
Solution Approach 2:
The method performs preliminary enrichment of methylated DNA from cfDNA samples before sequencing. By pre-capturing methylated DNA fragments using methyl-binding domain proteins under optimized conditions, the protocol concentrates the scarce methylated signal from low-input samples, making subsequent sequencing feasible and accurate
2Quantity of substance
If whole-genome sequencing is performed on cfDNA to detect cancer-specific alterations, then comprehensive genomic coverage is achieved, but the low abundance of methylated DNA limits sensitivity
Solution Approach 1:
The patent extracts and enriches specifically for methylated DNA fragments from the total cfDNA population using methyl-binding domain proteins. This extraction step isolates the rare methylated molecules (which carry cancer-specific epigenetic information) from the overwhelming background of unmethylated DNA, thereby concentrating the signal and improving detection sensitivity while maintaining genomic coverage
Solution Approach 2:
Methyl-binding domain proteins serve as intermediary molecules that selectively bind to methylated DNA sequences. These intermediaries enable the specific capture and enrichment of methylated cfDNA fragments, allowing the method to achieve both comprehensive genomic coverage and high detection sensitivity by mediating between the low-abundance target and the sequencing platform
3Quantity of substance
If cfDNA samples with less than 100 ng of DNA are used for methylation analysis, then minimally invasive sampling is achieved, but existing techniques become impractical
Solution Approach 1:
The patent applies partial action by performing MeDIP-seq on a subset of cfDNA samples with very low input (less than 100 ng) rather than requiring bulk samples. The optimized protocol uses reduced reagent volumes and adjusted incubation times to achieve sufficient enrichment of methylated DNA from these partial samples, making the technique feasible for minimally invasive applications
Solution Approach 2:
The method changes multiple parameters to accommodate low-input samples: reducing protein A bead volumes, adjusting antibody-to-DNA ratios, optimizing sonication energy input, and modifying purification bead concentrations. These parameter changes collectively enable the protocol to work effectively with less than 100 ng of cfDNA while maintaining technique feasibility
4Measurement precision
If DNA is fragmented to less than 200 bp in length for cfDNA analysis, then accurate representation of circulating DNA is achieved, but traditional methods like RRBS become impossible to perform
Solution Approach 1:
The patent performs MeDIP enrichment of methylated DNA fragments before any size selection or library preparation steps. By conducting the methyl-binding domain protein incubation and capture on the fragmented cfDNA samples first, the method preserves the native size distribution (including fragments less than 200 bp) and enables downstream sequencing without requiring size enrichment that would exclude small fragments
Solution Approach 2:
The patent inverts the traditional workflow by performing methylation enrichment (MeDIP) before library preparation and size selection, rather than preparing libraries first and then attempting to enrich for methylated sequences. This inversion allows the method to work with fragmented DNA of any size, including fragments less than 200 bp, making the approach compatible with cfDNA characteristics while maintaining accurate representation
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
cfMeDIP-seq enhances the sensitivity and efficiency of detecting cancer-specific DNA methylation patterns, allowing for accurate identification and monitoring of malignant diseases with reduced sequencing costs.
Implementation Method 1
a binder selective for methylated polynucleotides
Data Source
AI summary
There is described herein, a method of capturing cell-free methylated DNA from a sample having less than 100 mg of cell-free DNA, comprising the steps of: subjecting the sample to library preparation to permit subsequent sequencing of the cell-free methylated DNA; adding a first amount of filler DNA to the sample, wherein at least a portion of the filler DNA is methylated; denaturing the sample; and capturing cell-free methylated DNA using a binder selective for methylated polynucleotides.