DNMT3B shapes the mCA landscape and regulates mCG for promoter bivalency in human embryonic stem cells

DNMT3B is known as a de novo DNA methyltransferase. However, its preferential target sites for DNA methylation are largely unknown. Our analysis on ChIP-seq experiment in human embryonic stem cells (hESC) revealed that DNMT3B, mCA and H3K36me3 share the same genomic distribution profile. Deletion of DNMT3B or its histone-interacting domain (PWWP) demolished mCA in hESCs, suggesting that PWWP domain of DNMT3B directs the formation of mCA landscape. In contrast to the common presumption that PWWP guides DNMT3B-mediated mCG deposition, we found that deleting PWWP does not affect the mCG landscape. Nonetheless, DNMT3B knockout led to the formation of 2985 de novo hypomethylated regions at annotated promoter sites. Upon knockout, most of these promoters gain the bivalent marks, H3K4me3 and H3K27me3. We call them spurious bivalent promoters. Gene ontology analysis associated spurious bivalent promoters with development and cell differentiation. Overall, we found the importance of DNMT3B for shaping the mCA landscape and for maintaining the fidelity of the bivalent promoters in hESCs.