Variant PRC1 complex-dependent H2A ubiquitylation drives PRC2 recruitment and polycomb domain formation.
Bottom Line: Chromatin modifying activities inherent to polycomb repressive complexes PRC1 and PRC2 play an essential role in gene regulation, cellular differentiation, and development.Here, using a de novo targeting assay in mouse embryonic stem cells we unexpectedly discover that PRC1-dependent H2AK119ub1 leads to recruitment of PRC2 and H3K27me3 to effectively initiate a polycomb domain.This activity is restricted to variant PRC1 complexes, and genetic ablation experiments reveal that targeting of the variant PCGF1/PRC1 complex by KDM2B to CpG islands is required for normal polycomb domain formation and mouse development.
Affiliation: Laboratory of Chromatin Biology and Transcription, Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK.Show MeSH
Mentions: To examine the possibility that H2AK119ub1 may play a general role in PRC2 localization and activity at normal polycomb target sites, we exploited a Ring1a−/−Ring1bfl/fl mouse ESC system, in which H2AK119ub1 can be rapidly depleted by removing the catalytic core of all PRC1 complexes (RING1A/B) through addition of the drug tamoxifen, without disrupting the cellular protein levels of PRC2 components (Endoh et al., 2008) (Figures 4A–4C). Following RING1A/B deletion, ChIP-sequencing revealed a clear loss of SUZ12, EZH2, and H3K27me3 at individual genes (Figures 4D and S2A) and at target sites genome-wide (Figure 4E and 4F). Indeed, 85% of SUZ12 and 83% of EZH2 sites showed a greater than 1.5-fold reduction in occupancy after PRC1 removal (Figures 4G and S3A). A closer inspection of SUZ12 sites defined as having a less than 1.5-fold change in PRC2, revealed that these sites do exhibit an observable loss in PRC2 binding (Figure S3B, S3C, and S3D) suggesting that most PRC2 sites are affected by loss of PRC1 activity. These effects on PRC2 occupancy were seemingly independent of high-level gene reactivation, as PRC2 reductions occurred at genes displaying small or large fluctuations in gene expression (Figures S2B and S2C).
Affiliation: Laboratory of Chromatin Biology and Transcription, Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK.