Polycomb-Dependent Regulatory Contacts between Distant Hox Loci in Drosophila

SummaryIn Drosophila melanogaster, Hox genes are organized in an anterior and a posterior cluster, called Antennapedia complex and bithorax complex, located on the same chromosome arm and separated by 10 Mb of DNA. Both clusters are repressed by Polycomb group (PcG) proteins. Here, we show that genes of the two Hox complexes can interact within nuclear PcG bodies in tissues where they are corepressed. This colocalization increases during development and depends on PcG proteins. Hox gene contacts are conserved in the distantly related Drosophila virilis species and they are part of a large gene interaction network that includes other PcG target genes. Importantly, mutations on one of the loci weaken silencing of genes in the other locus, resulting in the exacerbation of homeotic phenotypes in sensitized genetic backgrounds. Thus, the three-dimensional organization of Polycomb target genes in the cell nucleus stabilizes the maintenance of epigenetic gene silencing.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (146 K)Download as PowerPoint slideHighlights► A subset of Polycomb target genes frequently colocalize within Drosophila nuclei ► Hox gene contacts depend on Polycomb proteins and are evolutionarily conserved ► Specific regulatory DNA elements affect Hox gene contacts ► Decrease of Hox gene contacts reduces silencing