Mus musculus Transcriptome or Gene expression. Mus musculus

Histone H3 lysine 9 trimethylation (H3K9me3) is a key epigenetic modification required for heterochromatin formation and maintenance, genome stability and silencing of transposable elements in embryonic stems cells (ESCs). The H3K9-specific methyltransferase (KMT) SETDB1 is vital for mammalian development as it regulates ESCs pluripotency in the early embryo. Here we unravel that SETDB1 undergoes automethylation on two lysines, embedded within its catalytic domain, both in vitro and in cells. Importantly, SETDB1 automethylation is required for mouse ESCs stemness, growth and viability. Interestingly, this automethylation does not seem to regulate SETDB1 catalytic activity but its interaction with many chromodomain-containing partners. This includes the Heterochromatin Protein 1 gamma (HP1γ), which binds H3K9me3 thereby leading to the spreading and maintenance of H3K9me3 at heterochromatin. Hence, genome-wide analyses show that the integrity of the two SETDB1 automethylated lysines is required for both coding genes and transposable elements silencing in mESCs. Indeed, our data show that automethylation-deficient SETDB1 expression leads to a lack of H3K9me3 establishment and subsequent HP1γ recruitment at target loci. Taken together, our findings uncover a novel mechanism regulating SETDB1 KMT key functions that are key in embryonic stems cells identity maintenance.