Oxidative Bisulfite Sequencing: An Experimental and Computational Protocol.

Area of Science:

• Epigenetics
• Molecular Biology
• Genomics

Background:

• Bisulfite sequencing (BS-seq) is the gold standard for DNA methylation mapping but cannot distinguish between 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC).
• Oxidative bisulfite sequencing (oxBS-seq) was developed to enable absolute quantification of both 5mC and 5hmC.
• Existing oxBS-seq protocols require optimization for accuracy and compatibility with modern sequencing technologies.

Purpose of the Study:

• To provide a detailed, updated laboratory protocol for oxidative bisulfite sequencing (oxBS-seq).
• To present a bioinformatics pipeline for analyzing whole-genome oxBS-seq data generated from Illumina short-read sequencing.
• To enable accurate, single-base resolution discrimination of 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC).

Main Methods:

• Utilized potassium perruthenate (KRuO4) as the oxidant for selective oxidation of 5hmC prior to bisulfite treatment.
• Implemented a modified oxBS-seq protocol for whole-genome DNA methylation analysis.
• Developed and applied a bioinformatics pipeline tailored for processing Illumina short-read sequencing data from oxBS-seq experiments.

Main Results:

• The updated oxBS-seq protocol allows for the direct readout of 5mC after oxidation of 5hmC.
• Comparison of oxBS-seq and BS-seq data enables accurate inference of 5hmC levels.
• The described bioinformatics pipeline effectively handles large-scale whole-genome oxBS-seq data.

Conclusions:

• The optimized oxBS-seq protocol and associated bioinformatics pipeline provide a robust method for absolute quantification of 5mC and 5hmC.
• This technique advances the study of DNA methylation dynamics at single-base resolution.
• The methodology is crucial for epigenomic research requiring precise differentiation of cytosine modifications.