Parallel PRC2/cPRC1 and vPRC1 pathways silence lineage-specific genes and maintain self-renewal in mouse embryonic stem cells

The transcriptional repressors Polycomb Repressive Complex 1 (PRC1) and PRC2 are required to maintain cell fate during embryonic development. PRC1 and PRC2 catalyse distinct histone modifications, establishing repressive chromatin at shared targets. Loss of PRC1, but not PRC2, from mouse embryonic stem cells (mESCs) triggers exit from pluripotency. How PRC2 and PRC1, which consists of distinct “variant PRC1” (vPRC1) and “canonical PRC1” (cPRC1) complexes, cooperate to silence genes and support mESC self-renewal is unclear. Here, we report that independent pathways composed of vPRC1 and cPRC1/PRC2 repress shared target genes. Individual loss of vPRC1, cPRC1, or PRC2 disrupts only one pathway and does not impair mESC pluripotency. However, loss of both pathways leads to mESC differentiation and activation of a subset of poised target genes co-occupied by relatively high levels of PRC1/PRC2. Thus, parallel pathways explains the differential requirements for PRC1 and PRC2, and provides robust silencing of poised, lineage-specific genes.