Genome-scale DNA methylation maps of pluripotent and differentiated cells

We report the generation and analysis of genome-scale DNA methylation profiles at nucleotide resolution in mammalian cells. Using high-throughput Reduced Representation Bisulfite Sequencing (RRBS) and single-molecule-based sequencing, we generated DNA methylation maps covering the vast majority of CpG islands, and a representative sampling of conserved non-coding elements, transposons and other genomic features, for murine embryonic stem (ES) cells, ES-derived and primary neural cells, and eight other primary tissues. Several key findings emerge from the data. First, DNA methylation patterns are better correlated with histone methylation patterns than with the underlying genome sequence context. Second, methylation of CpGs are dynamic epigenetic marks that undergo extensive changes during cellular differentiation, particularly in regulatory regions outside of core promoters. Third, analysis of ES-derived and primary cells reveals that 'weak' CpG islands associated with a specific set of developmentally regulated genes undergo aberrant hypermethylation during extended proliferation in vitro, in a pattern reminiscent of that reported in some primary tumors. More generally, the results establish RRBS as a powerful technology for epigenetic profiling of cell populations relevant to developmental biology, cancer and regenerative medicine. Keywords: High-throughput Reduced Representation Bisulfite Sequencing (RRBS), Illumina, cell type comparison