MOLECULAR GENETICS OF DOSAGE COMPENSATION IN DROSOPHILA

发生剂量补偿以平衡男性中的X连锁基因表达 (XY)和女性（XX），并且在许多利用 性别决定的染色体基础。 在果蝇中，剂量 补偿主要是通过增加X-连锁的 男性的基因 赋予性别特异性的基因开关是 关键：缺乏X染色体超转录杀死男性，而 不适当的X超转录会杀死女性 最近的研究表明 剂量补偿需要一个独特的染色质环境， 雄性X. 四种调节蛋白（MSL蛋白）和一种特异性乙酰化的 组蛋白H4亚型（H4 Ac 16）以条带模式沿着 而不是沿着常染色体或女性X染色体。 的 这些蛋白质的存在与不同的细胞学 雄性X的出现，以及其增加的转录活性。 我们的实验重点是MSL蛋白的功能和调节。 我们将分析剂量补偿的机制，作为 通过染色质环境协调基因的调节。 我们将 还剖析了调节剂量补偿的遗传开关。 具体目标是：一。分析特定地点之间的联系 组蛋白乙酰转移酶活性和剂量补偿。 二. 鉴定赋予X染色体的顺式作用位点- 对MSL蛋白质的特异性。 三.特定性别的定义 调节剂量补偿的机制。 四.鉴定 使用新的遗传筛选的额外剂量补偿调节剂。 诉 MSL非依赖性剂量补偿中的性致死作用分析。 生物化学和遗传学方法都将被利用。 生化 研究将集中于鉴定一种男性特异性组蛋白H4 乙酰转移酶活性及其与MSL蛋白的关系。 MSL蛋白的染色质靶点的定义将解决基础 因为它们对X染色体的特异性 转基因实验将 剖析先前克隆的msl基因的调控和功能。 新的遗传筛选将利用转基因表型来识别 剂量补偿所需的新功能。 了解MSL蛋白的功能和调节方式可能有助于 与基因在高等生物发育过程中的控制方式有关。 MSL蛋白质在功能性免疫应答的建立和维持中起作用。 染色质的状态，这是一个研究的前沿课题， 转录调控 此外，性别特异性调节 MSL蛋白为遗传开关提供了一种新的模型。 双峰 最初在果蝇等模式生物中发现的转换机制 在许多情况下与人类的正常和疾病状态有关。

Dosage compensation occurs to equalize X-linked gene expression in males (XY) and females (XX), and is essential in many organisms that utilize a chromosomal basis for sex determination. In Drosophila, dosage compensation occurs primarily by increasing transcription of X-linked genes in males. The genetic switch that confers sex-specificity is critical: lack of X chromosome hypertranscription kills males, while inappropriate X hypertranscription kills females. Recent studies suggest that dosage compensation requires a distinct chromatin environment on the male X. Four regulatory proteins (MSL proteins) and a specific acetylated isoform of histone H4 (H4Ac16) are associated in a banded pattern along the male X and not along the autosomes or the female X chromosomes. The presence of these proteins correlates with the distinct cytological appearance of the male X, and its increased transcriptional activity. Our experiments focus on the function and regulation of the MSL proteins. We will analyze the mechanism of dosage compensation as a model for the coordinate regulation of genes by their chromatin environment. We will also dissect the genetic switch by which dosage compensation is regulated. The specific aims are: I. Analysis of the link between site-specific histone acetyltransferase activity and dosage compensation. II. Identification of the cis-acting sites that confer X chromosome- specificity to the MSL proteins. III. Definition of the sex-specific mechanism that regulates dosage compensation. IV. Identification of additional dosage compensation regulators using novel genetic screens. V. Analysis of sex lethal action in MSL-independent dosage compensation. Both biochemical and genetic approaches will be utilized. The biochemical studies will focus on identification of a male-specific histone H4 acetyltransferase activity, and its relationship to the MSL proteins. Definition of chromatin targets of the MSL proteins will address the basis for their exquisite X chromosome specificity. Transgenic experiments will dissect the regulation and function of the previously cloned msl genes. Novel genetic screens will capitalize on transgenic phenotypes to identify new functions required for dosage compensation. Understanding how the MSL proteins function and are regulated is likely to relate to how genes are controlled during development in higher organisms. The MSL proteins act in the establishment and maintenance of functional states of chromatin, which is a subject at the frontier of research on transcriptional regulation. In addition, the sex-specific regulation of the MSL proteins provides a new model for a genetic switch. Bi-modal switch mechanisms found initially in model organisms such as fruitflies are in many cases relevant to normal and disease states in humans.