MOLECULAR GENETICS OF DOSAGE COMPENSATION IN DROSOPHILA

剂量补偿是为了平衡男性X连锁基因的表达 (XY)和雌性(XX)，在许多利用 性别决定的染色体基础。在果蝇中，剂量 补偿主要通过增加X-连锁的转录来实现 男性体内的基因。赋予性别专一性的基因开关是 关键：缺乏X染色体超转录会导致男性死亡，而 不适当的X基因过度转录会杀死雌性。最近的研究表明 这种剂量补偿需要一个明显的染色质环境 雄性X.四种调节蛋白(MSL蛋白)和一种特定的乙酰化蛋白 组蛋白H4(H4Ac16)的异构体沿 雄性X染色体，而不是沿着常染色体或雌性X染色体。这个 这些蛋白的存在与不同的细胞学相关 雄性X的出现，以及它的转录活性增加。 我们的实验重点是MSL蛋白的功能和调控。 我们将分析剂量补偿的机制，作为一种模型 通过染色质环境协调基因的调节。我们会 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与剂量补偿。二、 X染色体顺式作用位点的鉴定-- MSL蛋白的特异性。三、按性别区分的定义 调节剂量补偿的机制。四、身份识别 使用新型基因筛选的额外剂量补偿调节器。五. MSL非依赖剂量补偿中性致死行为的分析。 生物化学和遗传方法都将被利用。生物化学 研究将集中在鉴定一种男性特有的组蛋白H4 乙酰转移酶的活性及其与MSL蛋白的关系。 MSL蛋白染色质靶标的定义将解决基础问题 因为他们精致的X染色体专一性。转基因实验将会 对已克隆的msl基因的调控和功能进行剖析。 新的基因筛查将利用转基因表型来识别 剂量补偿所需的新功能。 了解MSL蛋白是如何发挥作用和受到调控的可能会 与高等生物体发育过程中基因如何控制有关。 MSL蛋白在功能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，针对性别的规定 MSL蛋白为基因转换提供了一种新的模型。多式联运 最初在果蝇等模式生物中发现的开关机制 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.