GSE209956
Chromatin organization in 3D distinguishes the influences of dMes-4/NSD and Hypb/dSet2 in protecting genes from H3K27me3 silencing [Hi-C]
Maintenance of gene expression programs requires cell-type specific barcoding of genomes through euchromatin interspaced with facultative heterochromatin domains where PRC1/2 hinder chromatin accessibility thereby repressing genes inside such domains. At heterochromatin-euchromatin borders, regulation of heterochromatin spreading may depend on transcriptional activity, histone modifiers, and chromatin barrier insulators or the borders of topological associated domain (TADs). Here we show that depletion of H3K36 di- or tri-methyl histone methyl transferases dMes-4/NSD or Hypb/dSet2 induces H3K27me3 spreading at H3K27me3 borders, accounting for the repression of hundreds of genes upon depletion of these enzymes. dMes-4/NSD influences genes within active chromatin hubs and flanked by H3K27me3 borders demarcated by a TAD border, unlike dHypb/dSet2 that protects genes near H3K27me3 borders in absence of a TAD border. Insulator mutants that disrupt 3D chromatin hubs recapitulate only the H3K27me3 spreading observed upon depletion of dMes-4/NSD, and not of Hypb/dSet2. Hi-C data demonstrate how dMes-4/NSD directly block the propagation of the long-range interactions marking the inactive TADs, onto neighbor active regions, unlike Hypb/dSet2. Our data thus show a division of labor between dMes-4/NSD and Hypb/dSet2 to protect genes against H3K27me3 silencing, highlighting a direct influence of H3K36me marks on the demarcation of H3K27me3 domains within repressive TADs. Overall design: We used the technology of Hi-C to quantify long-range interactions and chromosome conformation in order to describe topological domains in presence or absence of H3K36 HMTs.Chromatin extracted from cells in wild-type or after a knock-down of HypB or Mes4