The analysis of genome-wide epigenomic alterations including DNA methylation has become a subject of intensive research for many complex diseases. Whole-genome bisulfite sequencing (WGBS) using next-generation sequencing technologies can be considered the gold standard for a comprehensive and quantitative analysis of cytosine methylation throughout the genome. Several approaches including tagmentation- and post bisulfite adaptor tagging (PBAT)-based WGBS have been devised. Here, we provide a detailed protocol based on a commercial kit for the preparation of libraries for WGBS from limited amounts of input DNA (50-100 ng) using the classical approach of WGBS by ligation of methylated adaptors to the fragmented DNA prior to bisulfite conversion. The converted library is then amplified with an optimal number of PCR cycles to ensure high sequence diversity and low duplicate rates. Spike-in of unmethylated DNA allows for the precise estimation of bisulfite conversion rates. We also provide a step-by-step description of the data analysis using publicly available bioinformatic tools. The described protocol has been successfully applied to different human samples as well as DNA extracted from plant tissues and yields robust and reproducible results.
Keywords: Bisulfite conversion; DNA methylation; Data analysis; Low-input; Spike-in; Whole-genome bisulfite sequencing.