Distinct Roles of H3K27me2 and H3K27me3 States Unveiled By Fate Specification of Embryonic Stem Cells

The Polycomb Repressive Complex 2 (PRC2) induces methylation of lysine 27 of histone H3 (H3K27) through its catalytic subunit Ezh2. PRC2-mediated di- and tri-methylation (H3K27me2/me3) have been interchangeably associated with gene repression. However, it remains unclear whether these two degrees of H3K27 methylation have indeed different functions. In this study, we have generated isogenic mouse embryonic stem cells (ESC) with a modified H3K27me2/H3K27me3 ratio. Our findings document a developmental dynamic control in the genomic distribution of H3K27me2 and H3K27me3 at regulatory regions in ESC. They also reveal that modifying the H3K27me2/H327me3 ratio is sufficient for the acquisition and repression of defined cell lineage transcriptional programs and phenotypes, along with influencing induction of the ESC ground state. Overall design: To establish the role of H3K27me2 and H3K27me3 ratio balance in ES cell differentiation, we constructed a mutant ES cell line by TALEN which carries a hyperactive form of Ezh2 that changes the ratio of H3K27me2 and H3K27me3 . The distribution of H3K27 methylation status (H3K27me1, H3K27me2, H3K27me3) and other histone marks (H3K4me1, H3K27ac) were examined by ChIP-seq (2 replicates each) along with gene expression profiles by RNA-seq (3 replicates each) in wild type ES cells, mutant ES cells,ES cells differentated for 24 hours, ES cells differentiated to embryoid bodies and C2C12 skeletal muscle cell line. To understand the affect of H3K27me2/H3K27me3 ratio change during ES cell ground state transition, RNA expression profiles were examined in ground state wild type and mutant ES cells by RNA-seq (3 replicates)