The transcription factor M1BP targets CP190 to chromatin to regulate transcription and chromatin insulator activity (ChIP-Seq)

Chromatin insulators are DNA-protein complexes that establish distinct higher order transcriptional domains. In Drosophila, CP190 is the only common factor for all the DNA-binding insulator protein complex. Insulators harbour two properties: they can block communication between an enhancer and a promoter, and also act as a barrier between heterochromatin and euchromatin. In Drosophila, the gypsy insulator complex contains three core components; Su(Hw), CP190 and Mod(mdg4)67.2. In our studies, using mass-spec analysis and of immunopurified complexes from Drosophila embryonic nuclear extracts, we identified the transcription factor Motif 1 Binding Protein (M1BP) associated with CP190 and verified this interaction by coimmunoprecipitation. Furthermore, depletion of M1BP results in loss of both enhancer-blocking and barrier activities, also disrupts the nuclear localization of CP190-marked insulator bodies within the developing fly. ChIP-seq analysis of both factors in Kc167 cultured hemocytes revealed extensive overlap of the two factors, particularly at Motif 1 containing promoters. Depletion of M1BP results in extensive loss of CP190 chromatin association, and depletion of CP190 also greatly affects M1BP chromatin association. Moreover, EU-seq analysis after depletion of either CP190 or M1BP suggests they regulate gene expression in similar fashion. Further analysis using reporter assays verifies that CP190-dependent gene expression changes are dependent on the presence of Motif 1. Our results suggest a novel mechanistic relationship between CP190 and M1BP function with respect to transcriptional regulation and higher order chromatin organization. Overall design: Examination of overlapping of M1BP with insulator proteins Su(Hw), CP190 and Mod(mdg4) genome wide in Kc167 embryonic cell lines and also to investigate whether association of these insulator factors are dependent on M1BP or binding of M1BP dependent on CP190.