Molecular Genetics of Dosage Compensation in Drosophila

剂量补偿是基因特异性调控和基因调控之间相互作用的一个明显例子。 染色体结构。这一过程已经进化到使X连锁基因在男性中的表达等同于 有一条X染色体，雌性有两条。在分子水平上检查的物种中，剂量 补偿是通过修饰X染色体的性别特有因素来调节的。在果蝇中，剂量 补偿至少部分是通过组蛋白H4乙酰化实现的，这种乙酰化受雄性- 由MSL蛋白和非编码Rox RNA组成的特定的X-特异性核糖核蛋白复合体。我们的 在接下来的赠款期间，重点将是了解染色质激活是如何定向和传播的 一条染色体。我们目前的数据表明，非编码Rox RNA合成的位点起到了成核作用 用于MSL复合体在独联体中的传播。 我们的实验将测试MSL复合体的分布模型，在该模型中，来自Rox的局部扩散在顺式中 在反式中，基因与扩散到更多的位置是平衡的。我们将分析MSL复合体的动力学 X的建立和维持，以及MSL复合体对Rox RNA的自动调节。我们的模型 MSL复合体的传播引起了与哺乳动物剂量补偿的有趣的相似之处。在这两个地方 苍蝇和人类，调节分子通常被限制在顺式X染色体上，但如果被带到 常染色体，可以在从未补偿过剂量的基因上传播。染色质的组织 核化部位的结构域可能是基因组调控的一种重要的一般机制。 功能。因此，剖析这些以染色质为基础的调控过程的机制应该 洞察许多重要的生物学问题，包括人类的正常和疾病状态。 多线染色体的极高空间分辨率和蛋白质和蛋白质中突变体的可用性 RNA传播组件使MSL复合体成为确定变化方式的优秀模型系统 染色质结构影响复杂生物体的基因表达。

Dosage compensation is a striking example of the interplay between gene-specific regulation and chromosomal architecture. This process has evolved to make X-linked gene expression equivalent in males with one X chromosome and females with two. In species examined at the molecular level, dosage compensation is mediated by sex-specific factors that decorate the X chromosomes. In Drosophila, dosage compensation is achieved, at least in part, through site-specific histone H4 acetylation, modulated by a male- specific, X-specific ribonucleoprotein complex composed of MSL proteins and non-coding roX RNAs. Our focus in the coming grant period will be to understand how chromatin activation is targeted and spread along a chromosome. Our current data suggest that sites of noncoding roX RNA synthesis act as nucleation sites for spreading of MSL complexes in cis. Our experiments will test a model for distribution of MSL complexes in which local spreading in cis from roX genes is balanced with diffusion to additional sites in trans. We will analyze the dynamics of MSL complex establishment and maintenance on the X, and autoregulation of roX RNA by MSL complexes. Our model for spreading of MSL complexes raises interesting parallels with mammalian dosage compensation. In both flies and humans, regulatory molecules are normally restricted in cis to the X chromosome, but if brought to autosomes, can spread on genes never before dosage compensated. The organization of chromatin domains by nucleation sites is likely to be an important general mechanism for regulation of genome function. Thus, dissecting the mechanisms underlying these chromatin-based regulatory processes should provide insight into many important biological problems, including normal and disease states in humans. The superb spatial resolution of polytene chromosomes and the availability of mutants in the protein and RNA spreading components make the MSL complex an excellent model system to determine how changes in chromatin architecture affect gene expression in complex organisms.