Genetic and physical interaction of Drosophila Ino80 with Polycomb Responsive Element

Abstract

AbstractThe chromatin remodeling protein, dIno80 (DrosophilaIno80) regulates homeotic genes. We show that Ino80, along with Trx and ETP (Enhancer of Trithorax and Polycomb) proteins, interacts with two Polycomb/Trithorax Responsive Elements (PRE/TRE),iab-7andbxd PREin flies and the larval imaginal discs. In S2 cells, dIno80 localizes to the endogenousiab-7andbxd-PREs. The localization of Ino80 and Pleiohomeotic (Pho) at the PRE is sensitive to the cellular abundance of each other; when levels ofIno80are limiting, there is increased Pho enrichment, andPhoknock-down leads to increased enrichment of Ino80. We demonstrate that over-expression of dIno80 rescues the pupal lethality inpleiohomeotic(pho) deficient flies, which suggests that dIno80 has a role in cellular memory. The apparent competition between Pho and Ino80 for binding at the PRE indicates that Ino80 may act as a potential recruiter of the regulatory complex in addition to being a chromatin remodeler.Author SummaryThe null mutants of Pho and dIno80 show lethality at different stages of development in the fly, implying that they may function independent of each other. The observation that Pho-lethality can be rescued by overexpression of dIno80 with significant penetrance and that Ino80 has its own DNA binding domain, led us to predict that Ino80 may have Pho-independent functions, perhaps through non-canonical complexes. In the current study, we show that dIno80 interacts withbxdandiab-7PRE in cooperation with Polycomb and Trithorax proteins and regulate the homeotic genes. The effect of knock-down or mutation of dIno80 results in altered phenotype in adult flies and rescue of Lac-Z expression in imaginal discs, in parallel with similar effect of Pho mutation or knock-down. We provide evidence of direct interaction of dIno80 withiab7-andbxd-PRE using chromatin immunoprecipitation. The dIno80 localization in and around the PRE sequence was enhanced in the absence of Pho, indicating competition between Pho and dIno80 for binding at the PRE.