Molecular Genetics of Dosage Compensation in Drosophila

剂量补偿是基因特异性调节和 染色体结构这一过程已经发展到使X连锁基因表达在男性中等同 只有一条X染色体的女性有两条在分子水平上检查的物种中， 补偿是由修饰X染色体的性别特异性因子介导的。在果蝇中，剂量 补偿至少部分地通过位点特异性组蛋白H4乙酰化来实现，其由雄性- 由MSL蛋白和非编码roX RNA组成的特异性X特异性核糖核蛋白复合物。我们 在接下来的资助期内，重点将是了解染色质激活是如何定向和沿着扩散的 一个染色体我们目前的数据表明，非编码roX RNA合成的位点作为成核位点， 用于顺式扩散MSL复合物。 我们的实验将测试MSL复合物分布的模型，其中局部顺式扩散来自roX 基因是平衡的扩散到额外的网站在反式。我们将分析的动态MSL复杂 X的建立和维持，以及MSL复合物对roX RNA的自动调节。我们的模型 MSL复合物的传播与哺乳动物剂量补偿产生了有趣的相似之处。无论是 调节分子通常限制在X染色体的顺式，但如果将其引入 常染色体，可以在基因上传播，从来没有剂量补偿。染色质的组织 核化位点的结构域可能是基因组调控的一个重要的一般机制 功能因此，解剖这些基于染色质的调控过程的机制应该 提供洞察许多重要的生物学问题，包括人类的正常和疾病状态。 多线染色体的高超空间分辨率和蛋白质中突变体的可用性， RNA扩散成分使MSL复合物成为确定如何改变的极好模型系统 在复杂生物体中影响基因表达。

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.