5hmC Detection via KMnO4 Oxidation and Bisulfite Sequencing
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Solution Overview
Problem
Current methods for detecting and distinguishing 5-hydroxymethylcytosine (5hmC) from 5-methylcytosine (5mC) and other cytosine modifications at single nucleotide resolution are limited by poor resolution, high sequencing errors, and inability to discriminate between these modifications using existing sequencing platforms.
Innovation Solution
A method involving oxidation of 5hmC to 5-formylcytosine (5fC) using a metal oxide, followed by bisulfite treatment and sequencing, allows for the identification of modified cytosine residues by producing distinct nucleotide sequences indicative of the modification type, applicable to all sequencing platforms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If enrichment methods with chemistry or antibodies are used for 5hmC detection, then 5hmC can be detected and quantified, but the resolution is poor (10s to 100s of nucleotides) and only relative quantitative information is obtained
Solution Approach 1:
The invention extracts 5hmC detection from complex enrichment procedures by using targeted oxidation with KMnO4 that specifically converts 5hmC to 5fC at single nucleotide positions, allowing direct sequencing without enrichment steps. This extraction approach isolates the detection function from the cumbersome enrichment process.
Solution Approach 2:
The invention changes the chemical state of 5hmC by oxidizing it to 5fC using KMnO4, creating a distinct chemical parameter difference that enables discrimination from 5mC and unmodified C during bisulfite sequencing. This parameter change transforms an undetectable modification into a sequencable signal.
2Measurement precision
If bisulfite sequencing is used to detect cytosine modifications, then single nucleotide resolution can be achieved, but 5mC and 5hmC cannot be discriminated because both deaminate very slowly
Solution Approach 1:
The invention performs preliminary oxidation of 5hmC to 5fC using KMnO4 before bisulfite treatment. This preliminary action creates a chemical distinction that will be revealed during sequencing, allowing 5hmC sites to be identified as C→T transitions while 5mC sites remain as C residues.
Solution Approach 2:
The invention introduces KMnO4 oxidation as an intermediary step between DNA extraction and bisulfite sequencing. This intermediary process converts 5hmC to 5fC, creating a detectable intermediate state that enables discrimination between 5mC and 5hmC that would otherwise be indistinguishable.
3Measurement precision
If single molecule real-time sequencing is used to detect 5hmC, then single nucleotide resolution can be achieved, but enrichment of DNA fragments is required which leads to loss of quantitative information and high sequencing errors
Solution Approach 1:
The invention extracts the detection capability from specialized single molecule sequencing platforms and transfers it to standard bisulfite sequencing platforms. By using chemical oxidation to create detectable differences, the invention eliminates the need for expensive, error-prone single molecule platforms while maintaining single nucleotide resolution.
Solution Approach 2:
The invention creates a chemical copy of the 5hmC modification signal by converting it to 5fC, which then produces a detectable C→T transition pattern during bisulfite sequencing. This copying approach allows standard sequencing platforms to detect modifications that would otherwise require specialized platforms.
4Quantity of substance
If pull-down approaches are used for 5hmC detection, then 5hmC can be enriched and detected, but only relative quantitative information is obtained and distributional biasing occurs during enrichment
Solution Approach 1:
The invention extracts 5hmC detection from enrichment-based pull-down approaches by using targeted oxidation that works on intact genomic DNA. This extraction eliminates the need for fragmentation and enrichment steps that introduce distributional biasing, allowing accurate quantification across the entire genome.
Solution Approach 2:
The invention changes the detection parameter from enrichment-based relative quantification to oxidation-based absolute quantification. By measuring the proportion of C→T transitions after KMnO4 treatment, the invention provides accurate quantitative information about 5hmC levels without the biasing effects of enrichment procedures.
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 accurate and precise identification and quantification of 5hmC, 5mC, and 5-formylcytosine at single nucleotide resolution, overcoming previous limitations in resolution and error rates, and is compatible with various sequencing techniques.
Implementation Method 1
oxidising said sample nucleotide sequence, thereby selectively oxidising said 5-hydroxymethylcytosine to 5-formylcytosine residues
Implementation Method 2
exploits the bisulfite-mediated deamination of cytosine to uracil
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
This invention relates to the modification of cytosine residues such as 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5fC) and allows them to be distinguished from cytosine (C) in a sample nucleotide sequence. Methods may comprise selectively oxidising or reducing a first portion of polynucleotides which comprise the sample nucleotide sequence and identifying the residues in the nucleotide sequence which corresponds to a 5-hydroxymethylcytosine (5hmC) or 5-formylcytosine (5fC) residue in the sample nucleotide sequence. These methods may be useful, for example in the analysis of genomic DNA and/or of RNA.