Fig. 2.

Bivalent histone modification in ES cells resolve during differentiation. In embryonic stem cell (ES cells), active mark histoneH3 lysine 4 di-methylation / tri-methylation (H3K4me2/3) and repressive mark histoneH3 lysine 27 trimethylation (H3K27me3) coexisted (bivalent modification status) on development-related genes, which might be necessary for sustaining an undifferentiated state. The bivalent modifications in their promoter regions resolved during ES cell differentiation into either H3K27me3 or H3K4me3 domains.