De Novo Polycomb Recruitment and Repressive Domain Formation

Abstract

Every cell of an organism shares the same genome; even so, each cellular lineage owns a different transcriptome and proteome. The Polycomb group proteins (PcG) are essential regulators of gene repression patterning during development and homeostasis. However, it is unknown how the repressive complexes, PRC1 and PRC2, identify their targets and elicit new Polycomb domains during cell differentiation. Classical recruitment models consider the pre-existence of repressive histone marks; still, de novo target binding overcomes the absence of both H3K27me3 and H2AK119ub. The CpG islands (CGIs), non-core proteins, and RNA molecules are involved in Polycomb recruitment. Nonetheless, it is unclear how de novo targets are identified depending on the physiological context and developmental stage and which are the leading players stabilizing Polycomb complexes at domain nucleation sites. Here, we examine the features of de novo sites and the accessory elements bridging its recruitment and discuss the first steps of Polycomb domain formation and transcriptional regulation, comprehended by the experimental reconstruction of the repressive domains through time-resolved genomic analyses in mammals.

Distinct roles for canonical and variant histone H3 lysine-36 in Polycomb silencing

“…Because H3K27 trimethylation at PREs is believed to be a prerequisite for the spread of this PTM into flanking regions [reviewed in ( 74 )], one might expect that if H3.2 and H3.3 functioned redundantly to enable PRC2 activity at PREs, then levels of H3K27me3 in the combined H3.3 K36R H3.2 K36R would be further diminished compared to what is observed in H3.3 WT H3.2 K36R animals. To test this idea, we performed Western blotting of L1 lysates from H3.3 WT H3.2 HWT (control), H3.3 WT H3.2 K36R , H3.3 K36R H3.2 HWT , and H3.3 K36R H3.2 K36R genotypes using anti-H3K27me3 antibodies, along with a pan-H3 loading control ( Fig.…”

Distinct roles for canonical and variant histone H3 lysine 36 in Polycomb silencing

“…Because H3K27 trimethylation at PREs is believed to be a prerequisite for the spread of this PTM into flanking regions (reviewed in ( 74 )), one might expect that if H3.2 and H3.3 functioned redundantly to enable PRC2 activity at PREs, levels of H3K27me3 in the combined H3.3 K36R H3.2 K36R would be further diminished compared to what is observed in H3.3 WT H3.2 K36R animals. To test this idea, we performed western blotting of first instar (L1) lysates from H3.3 WT H3.2 HWT (control), H3.3 WT H3.2 K36R , H3.3 K36R H3.2 HWT , and H3.3 K36R H3.2 K36R genotypes using anti-H3K27me3 antibodies, along with a pan-H3 loading control (Fig.…”

“…Because H3K27 trimethylation at PREs is believed to be a prerequisite for the spread of this PTM into flanking regions (reviewed in ( 74 )), one might expect that if H3.2 and H3.3 functioned redundantly to enable PRC2 activity at PREs, levels of H3K27me3 in the combined H3 . 3 K36R H3 .…”

Single-genome analysis reveals heterogeneous association of the Herpes Simplex Virus genome with H3K27me2 and the reader PHF20L1 following infection of human fibroblasts

“…We focused on H3K27me2, as this modification is also repressive to transcriptional activity (69, 70). Additionally, we considered that previous studies investigating the mechanisms of de novo Polycomb silencing in murine embryonic stem cells (mESCs) have shown full tri-methylation of H3K27 to take approximately 36 hours, a time frame inconsistent with the rapid events unfolding during early HSV-1 infection (67, 88, 89). However, the same studies demonstrate that H3K27me2 forms more rapidly.…”