EHMT2 represses totipotency- and differentiation-associated genes in pluripotent stem cells through distinct regulatory modes [ChIP]

Mouse embryonic stem cells (mESCs) and other naïve pluripotent stem cells, under specific conditions, can reverse typical developmental trajectories and de-differentiate into 2-cell-like cells (2CLCs) that resemble the mammalian embryo during zygotic genome activation (ZGA). We implemented a multipurpose allele for acute protein depletion and efficient immunoprecipitation to dissect the molecular functions of EHMT2 in mESCs. This approach allowed us to define different types of EHMT2 target genes and distinct modes of chromatin engagement and repression. Most notably, EHMT2 directly represses large clusters of co-regulated gene loci that comprise a significant fraction of the 2CLC-specific transcriptome by initiating H3K9me2 spreading from distal LINE-1 elements. Conversely, the loss of EHMT2 allows the recruitment of the activator DPPA2/4 to promoter-proximal ERVs in 2CLCs, thus facilitating the mESC-to-2CLC transition. Repression of germ layer-associated transcripts by EHMT2 occurs outside of gene clusters in collaboration with ZFP462 and entails binding to non-repeat enhancers. Our data suggests that EHMT2 functions as an attenuator of the bidirectional differentiation potential of mouse naïve pluripotent stem cells and define molecular models for the gene-specific repressive activity of this essential histone methyltransferase.