Massive redeployment of PRC1 proteins suppresses tumor formation during Drosophila development

Polycomb group proteins form two main complexes, PRC2 and PRC1, which generally coregulate their target genes. Here, we show that PRC1 components act as neoplastic tumor suppressors independently of PRC2 function. By mapping the distribution of PRC1 components and the histone H3K27me3 mark, we identify genes that acquire PRC1 and H3K27me3 in larvae, and a much larger set of genes bound by PRC1 in the absence of H3K27me3 in larval tissues. These genes massively outnumber canonical targets and they are preeminently involved in the regulation of cell proliferation, signaling and polarity. Mutation in PRC1 components specifically deregulates this set of genes, whereas canonical targets are derepressed in both PRC1 and PRC2 mutants. In human ES cells, PRC1 components colocalize with H3K27me3 like in Drosophila embryos, whereas they are selectively recruited to a large set of proliferation and signaling-associated genes in differentiated cell types, showing that the redeployment of PRC1 components during development is evolutionarily conserved. Overall design: Comparative study of Polycomb group proteins and histon marks during development with ChIP-Seq and RNA-Seq data in eye discs and wing discs (L3 stage) in Drosophila