Unique cell cycle-dependent variations in the pluripotent epigenetic landscape define novel cohorts of temporal expressed bivalent genes during hESCs differentiation

By mapping the genomic enrichments  of H3K4me3 and H3K27me3 modifications in pure populations of hESCs during the G2, mitotic and G1 phases of the cell cycle, we characterize cell cycle-dependent variations in the epigenetic landscape of bivalent genes, altering the current view of mitotic inheritance in pluripotent cells. We identified novel classes of bivalent domains that are highly enriched with H3K4me3 during mitosis, depleted during G1 only, and ubiquitously bivalent. These bivalent domains are associated with specific genes and expression patterns during differentiation. These cell cycle-dependent epigenetic profiles are unique to hESCs and are not observed following initiation of phenotype commitment. Our results establish a new dimension in cell cycle-dependent chromatin regulation that advances understanding of contributions the pluripotent epigenetic landscape to hESC identity.