Polycomb repressive complex PRC1 spatially constrains the mouse embryonic stem cell genome

Sarah Elderkin and colleagues show that PRC1 acts as a master regulator of genome architecture in mouse embryonic stem cells by organizing genes in three-dimensional interaction networks. They find that the strongest spatial network is composed of the four Hox clusters and key early developmental transcription factor genes, and they propose that selective release of genes from this spatial network underlies cell fate specification during embryonic development. The Polycomb repressive complexes PRC1 and PRC2 maintain embryonic stem cell (ESC) pluripotency by silencing lineage-specifying developmental regulator genes1. Emerging evidence suggests that Polycomb complexes act through controlling spatial genome organization2,3,4,5,6,7,8,9. We show that PRC1 functions as a master regulator of mouse ESC genome architecture by organizing genes in three-dimensional interaction networks. The strongest spatial network is composed of the four Hox gene clusters and early developmental transcription factor genes, the majority of which contact poised enhancers. Removal of Polycomb repression leads to disruption of promoter-promoter contacts in the Hox gene network. In contrast, promoter-enhancer contacts are maintained in the absence of Polycomb repression, with accompanying widespread acquisition of active chromatin signatures at network enhancers and pronounced transcriptional upregulation of network genes. Thus, PRC1 physically constrains developmental transcription factor genes and their enhancers in a silenced but poised spatial network. We propose that the selective release of genes from this spatial network underlies cell fate specification during early embryonic development.