Poised enhancers regulatory activity is topologically facilitated by polycomb [RNA-seq LHX5]

Poised enhancers marked by H3K27me3 in pluripotent cells were previously proposed to facilitate the establishment of somatic expression programs upon embryonic stem cell (ESC) differentiation. However, the functional relevance and mechanism of action of poised enhancers remain unknown. Here, we use genetic deletions to demonstrate that poised enhancers are necessary for the induction of major anterior neural regulators. Mechanistically, poised enhancers enable RNA Polymerase II recruitment to their cognate promoters upon differentiation. Interestingly, poised enhancers already establish physical interactions with their target genes in ESC in a Polycomb repressive complex 2 (PRC2) dependent manner. Loss of PRC2 led to neither the activation of poised enhancers nor the induction of their putative target genes in undifferentiated ESC. In contrast, loss of PRC2 severely and specifically compromised the induction of major anterior neural genes representing poised enhancer targets. Overall, our work illuminates a novel function for polycomb proteins, which we propose facilitate neural induction by providing major anterior neural loci with a permissive regulatory topology.