The Drosophila speciation factor HMR localizes to genomic insulator sites

Hybrid incompatibility between Drosophila melanogaster and D. simulans is caused by a lethal interaction of the proteins encoded by the Hmr and Lhr genes. In D. melanogaster the loss of HMR results in mitotic defects, an increase in transcription of transposable elements and a deregulation of heterochromatic genes. To better understand the molecular mechanisms that mediate HMR’s function, we measured genome-wide localization of HMR in D. melanogaster tissue culture cells by chromatin immunoprecipitation. Interestingly, we find HMR localizing to genomic insulator sites that can be classified into two groups. One group belongs to gypsy insulators and another one borders HP1a bound regions at active genes. The transcription of the latter group genes is strongly affected in larvae and ovaries of Hmr mutant flies. Our data suggest a novel link between HMR and insulator proteins, a finding that implicates a potential role for genome organization in the formation of species.黑腹果蝇（Drosophila melanogaster）与拟果蝇（Drosophila simulans）之间的杂交不亲和性，由Hmr基因与Lhr基因编码的蛋白质之间的致死性相互作用所导致。在黑腹果蝇中，HMR蛋白的缺失会引发有丝分裂缺陷、转座因子（transposable elements）的转录水平升高，以及异染色质基因的表达失调。为深入解析介导HMR发挥功能的分子机制，我们通过染色质免疫沉淀（chromatin immunoprecipitation）技术，检测了黑腹果蝇组织培养细胞中HMR的全基因组定位情况。值得注意的是，我们发现HMR可定位于基因组绝缘子位点，这类位点可分为两类：一类属于gypsy绝缘子（gypsy insulator），另一类则紧邻活跃基因上结合有异染色质蛋白1a（HP1a）的区域。在后一类基因中，其转录在Hmr突变果蝇的幼虫与卵巢内受到显著影响。本研究数据揭示了HMR与绝缘子蛋白之间的全新关联，这一发现暗示基因组组织在物种形成过程中或发挥潜在作用。