The analysis of genome-wide epigenomic alterations including DNA methylation and hydroxymethylation has become a subject of intensive research for many biological and disease-associated investigations. Whole-genome bisulfite sequencing (WGBS) using next-generation sequencing technologies is currently considered as the gold standard for a comprehensive and quantitative analysis of DNA methylation throughout the genome. However, bisulfite conversion does not allow distinguishing between cytosine methylation and hydroxymethylation requiring an additional chemical or enzymatic step to identify hydroxymethylated cytosines. Here we provide two detailed protocols based on commercial kits for the preparation of sequencing libraries for the comprehensive whole-genome analysis of DNA methylation and/or hydroxymethylation. If only DNA methylation is of interest, sequencing libraries can be constructed from limited amounts of input DNA by ligation of methylated adaptors to the fragmented DNA prior to bisulfite conversion. For samples with significant levels of hydroxymethylation such as stem cells or brain tissue, we describe the protocol of oxidative bisulfite sequencing (OxBs-seq), which in its current version uses a post-bisulfite adaptor tagging (PBAT) approach. Two methylomes need to be generated: a classic methylome following bisulfite conversion and analyzing both methylated and hydroxymethylated cytosines and a methylome analyzing only methylated cytosines, respectively. We also provide a step-by-step description of the data analysis using publicly available bioinformatic tools. The described protocols have been successfully applied to different human samples and yield robust and reproducible results.
Keywords: Bisulfite conversion; DNA methylation; Hydroxymethylation; Low input; Ovation® Methyl-seq; Oxidative bisulfite sequencing; PBAT; Spike-in; TrueMethyl® WholeGenome; Whole-genome bisulfite sequencing.