DNA methylation dynamics during early human development

DNA methylation is globally reprogrammed during mammalian preimplantation development, which has been well characterized in the mouse but not in other mammals. Here we report on the single base-resolution DNA methylome of human gametes and blastocysts. Near complete demethylation of the paternal genome was apparent, except for tandem repeat-containing CpG-rich regions, whereas the maternal genome was essentially resistant to replication-dependent global demethylation. The human oocyte methylome was characterized by a unique bimodal distribution of gene body methylation, a particular promoter methylation profile and a high proportion of hypomethylated transposable elements. Methylome and transcriptome comparisons between the human and mouse suggested species-specific regulation of many genes including the important DNA methylation regulators. Our findings are essential to understand the unique gene regulatory mechanisms during early human development and will facilitate preimplantation epigenetic diagnosis of human embryos.