Genome-wide profiling of Notch corepressor Hairless in Kc cells using Dam-ID

Several co-repressors interact directly with the DNA-binding protein CSL [Su(H) in Drosophila] and are proposed to keep target genes silenced in the absence of Notch activity. To investigate co-repressor activity in the context of this well defined signalling pathway, we analysed the genome-wide binding profile of the best-characterized CSL co-repressor in Drosophila, Hairless, in Kc cells and in wing imaginal discs. The binding profile in wing discs of a second CSL interacting repressor, SMRTER, was also analysed. There was significant overlap between Hairless and Su(H), both in Kc cells and in wing discs, where they were predominantly found in chromatin with active enhancer marks. The Hairless complex was widely present at some Notch regulated enhancers in the wing disc,but no binding was detected at others, indicating that it is not essential for silencing per se. Analysis of target enhancers confirmed differential requirements for Hairless. SMRTER binding significantly overlapped with Hairless, rather than complementing it, and many enhancers were apparently co-bound by both factors. Our analysis indicates that the actions of Hairless and SMRTER gate the enhancers to Notch activity and to Ecdysone signalling respectively, to ensure that the appropriate levels and timing of target gene expression are achieved. Three replicates from expression of Hairless-Dam fusion, 2 controls from DAM only