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Chromatin remodeling protein INO80 has a role in regulation of homeotic gene expression in Drosoph

Chromatin remodeling protein INO80 has a role in regulation of homeotic gene expression in Drosoph

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Chromatin remodeling protein INO80 has a role in regulation of homeotic gene expression in Drosophila Shipra Bhatia 1 , Hema Pawar 2 , Vasanthi Dasari 3 , Rakesh K. Mishra 3 , Shanti Chandrashekaran 2 * and Vani Brahmachari 1 * 1 Dr.B.R.Ambedkar Center for Biomedical Research, University of Delhi, Delhi 110007, India 2 Indian Agricultural Research Institute, New Delhi 110012, India 3 Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500007, India The homologues of yeast INO80 are identified across phyla from Caenorhabditis elegans to human. In Drosophila it has been shown that dINO80 forms a complex with Pleiohomeotic but does not interact with Hox PRE (polycomb responsive element). As some proteins of the INO80 complex are implicated in homeotic gene regulation, we examined if dINO80 is involved in regulation of homeotic genes. We find that dINO80 null mutants generated by imprecise excision of P-element are late embryonic lethals and show homeotic transformation. We detect misexpression of homeotic genes like Sex-comb reduced , Antennapedia , Ultrabithorax and Abdominal-B in dIno80 mutant embryos by immunostaining which is further substantiated by quantitative PCR. Polycomb phenotype in dIno80-Pc is enhanced in double mutants. Concur- rently, the localization of dINO80 to sequences upstream of misexpressed genes in vivo shows that dINO80 is involved in homeotic gene regulation and probably through its interactions with PcG-trxG complexes. Introduction The segmented pattern of the Drosophila embryo is established through hierarchical expression of gap, pair-rule, segment polarity and homeotic genes (Nusslein-Volhard & Wieschaus 1980). The tran- siently expressed segmentation genes establish homeo- tic gene expression whereas Polycomb (PcG) and trithorax group (trxG) genes maintain it (Qian et al. 1993). The PcG-trxG proteins work antagonistically and in their absence, the expression of homeotic genes is normal till just before gastrulation but at gas- trulation misexpression of all the homeotic genes is seen in all the segments. For instance, in a PcG mutant there is high and ubiquitous expression of Abdominal-B ( Abd-B ) throughout the germ band lead- ing to repression of all other homeotic genes. Conse- quently, all the abdominal segments resemble the eighth abdominal segment in morphology (Celniker et al. 1990). Conversely, the trxG genes positively regulate homeotic gene expression and are required for the normal expression of genes of the Antennapedia (ANT-C) and Bithorax (BX-C) complex. Embryos homozygous for lethal alleles of trithorax have posterior abdominal segments transformed to more anterior seg- mental identities. As expected, trxG mutant embryos and adults exhibit homeotic transformations similar to those seen in Sex combs reduced ( Scr ), Antennapedia ( Antp ), Ultrabithorax ( Ubx) , Abdominal - A ( abd-A ) and Abdominal-B ( Abd-B ) loss-of-function mutants (Ing- ham 1985). Genetic interaction data also support the antagonistic relationship between trxG and PcG genes (Kennison 1995). It is predicted that there are nearly 40 PcG-trxG proteins in Drosophila
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