GSE41950
Genome-wide localization of exosome components to active promoters and chromatin insulators in Drosophila
Chromatin insulators are functionally conserved DNA-protein complexes that are situated throughout the genome and organize independent transcriptional domains.  Previous work implicated RNA as an important cofactor in chromatin insulator activity, although the mechanisms by which RNA affects insulator activity are not yet understood.  Here we identify the exosome, the highly conserved major cellular 3' to 5' RNA degradation machinery, as a physical interactor of CP190-dependent chromatin insulator complexes in Drosophila.  High resolution genome-wide profiling of exosome by ChIP-seq in two different embryonic cell lines reveals extensive and specific overlap with the CP190, BEAF-32, and CTCF insulator proteins.  Colocalization occurs mainly at promoters but also well-characterized boundary elements, such as scs, scs', Mcp, and Fab-8.  Surprisingly, exosome associates primarily with promoters but not gene bodies, arguing against simple cotranscriptional recruitment to RNA substrates.  We find that exosome is recruited to chromatin in a transcription dependent manner, preferentially to highly transcribed genes.  Similar to insulator proteins, exosome is also significantly enriched at divergently transcribed promoters.  Directed ChIP of exosome in cell lines depleted of insulator proteins shows that CTCF is specifically required for exosome association at Mcp and Fab-8 but not other sites, suggesting that alternate mechanisms must also contribute to exosome chromatin recruitment.  Taken together, our results reveal a novel relationship between exosome and chromatin insulators throughout the genome. Overall design: ChIP-seq of exosome components. RNA-seq after control and exosome subunit knockdown in Drosophila cell lines.