Koya S Kiran, Meller Victoria H
Department of Biological Sciences, Wayne State University, Detroit, Michigan, United States of America.
PLoS One. 2015 Oct 15;10(10):e0140259. doi: 10.1371/journal.pone.0140259. eCollection 2015.
The ribonucleoprotein Male Specific Lethal (MSL) complex is required for X chromosome dosage compensation in Drosophila melanogaster males. Beginning at 3 h of development the MSL complex binds transcribed X-linked genes and modifies chromatin. A subset of MSL complex proteins, including MSL1 and MSL3, is also necessary for full expression of autosomal heterochromatic genes in males, but not females. Loss of the non-coding roX RNAs, essential components of the MSL complex, lowers the expression of heterochromatic genes and suppresses position effect variegation (PEV) only in males, revealing a sex-limited disruption of heterochromatin. To explore the molecular basis of this observation we examined additional proteins that participate in compensation and found that MLE, but not Jil-1 kinase, contributes to heterochromatic gene expression. To determine if identical regions of roX RNA are required for dosage compensation and heterochromatic silencing, we tested a panel of roX1 transgenes and deletions and find that the X chromosome and heterochromatin functions are separable by some mutations. Chromatin immunoprecipitation of staged embryos revealed widespread autosomal binding of MSL3 before and after localization of the MSL complex to the X chromosome at 3 h AEL. Autosomal MSL3 binding was dependent on MSL1, supporting the idea that a subset of MSL proteins associates with chromatin throughout the genome during early development. The broad localization of these proteins early in embryogenesis supports the idea of direct action at autosomal sites. We postulate that this may contribute to the sex-specific differences in heterochromatin that we, and others, have noted.
核糖核蛋白雄性特异性致死（MSL）复合体是黑腹果蝇雄性中X染色体剂量补偿所必需的。从发育3小时开始，MSL复合体结合转录的X连锁基因并修饰染色质。MSL复合体蛋白的一个子集，包括MSL1和MSL3，对于雄性而非雌性常染色体异染色质基因的完全表达也是必需的。MSL复合体的必需组成部分非编码roX RNA的缺失，仅在雄性中降低了异染色质基因的表达并抑制了位置效应斑驳（PEV），揭示了异染色质的性别受限破坏。为了探索这一观察结果的分子基础，我们研究了参与补偿的其他蛋白质，发现MLE而非Jil-1激酶有助于异染色质基因表达。为了确定剂量补偿和异染色质沉默是否需要相同区域的roX RNA，我们测试了一组roX1转基因和缺失，发现X染色体和异染色质功能可通过一些突变分离。对分期胚胎的染色质免疫沉淀显示，在胚胎发育晚期3小时MSL复合体定位于X染色体之前和之后，MSL3在常染色体上广泛结合。常染色体上的MSL3结合依赖于MSL1，支持了在早期发育过程中一部分MSL蛋白与整个基因组的染色质相关联的观点。这些蛋白质在胚胎发生早期的广泛定位支持了在常染色体位点直接作用的观点。我们推测，这可能导致了我们和其他人所注意到的异染色质中的性别特异性差异。
