TRANSCRIPTIONAL REGULATION BY X CHROMOSOME INACTIVATION

雌性真兽类进化出一种机制，使 每个体细胞中功能X连锁基因的剂量与雄性细胞的剂量相比。 这种剂量补偿是通过转录失活来完成的 女性两条X染色体中的一条上的基因。因此，对于大多数X链接的人来说 雌性体细胞中的基因，一种活跃和不活跃的等位基因驻留在 相同的核，但有不同的调控和表达。这个 X染色体失活过程在发育过程中受到调控 女性胚胎发育和涉及的坐标和染色体范围 顺式基因中X连锁基因的沉默。这个项目的长期目标是 探讨X染色体失活的分子机制。这 提案将调查分子基础以建立和 维持单个X连锁基因的差异表达， 次黄嘌呤磷酸核糖基转移酶(HPRT)基因的活性和 不活跃的X染色体。我们假设转录调控基因 通过X失活的HPRT基因将涉及一个复杂的相互作用层次。 依赖的监管机制，来自更高层次的长期效应 染色质结构，到启动子内的局部核小体结构和 其他调控区域，到单个序列特异的DNA蛋白 相互作用，每一种都对建立和 HPRT基因在活动期和非活动期维持差异表达的研究 不活跃的X染色体。我们进一步假设X的过程 染色体失活将通过这一层次的机制发挥作用 它调节X染色体上单个基因的转录。 因此，我们将对各种机制进行详细研究。 影响HPRT基因转录的基因。这项研究中提出的实验 应用程序将研究HPRT基因调控的两个方面，通过 X染色体失活。首先，我们将继续详细分析 在活性和非活性X染色体上的HPRT启动子区域，以及 DNA甲基化、局部染色质结构和序列的影响- 特异性DNA-蛋白质相互作用对启动子功能的影响。其次，我们将 开始对HPRT的结构和作用进行长期调查 染色质结构域在调节HPRT基因表达上的活性 和不活跃的X染色体。这将涉及到定义 域，然后识别和表征域中的元素 来调节它的染色质结构。了解以下机制 X失活调控单个X连锁基因的转录 应该提供洞察力和实验方法来研究 染色体和发育方面的这一独特的遗传过程。

Female eutherian mammals have evolved a mechanism which equalizes the dosage of functional X-linked genes in each somatic cell to that of males. This dosage compensation is accomplished by transcriptionally inactivating genes on one of the two X chromosomes in females. Thus, for most X-linked genes in female somatic cells, an active and inactive allele reside within the same nucleus but are differentially regulated and expressed. The process of X chromosome inactivation is developmentally regulated in female embryogenesis and involves the coordinate and chromosome-wide silencing of X-linked genes in cis. The long-term goal of this project is to determine the molecular mechanism of X chromosome inactivation. This proposal will investigate the molecular basis for establishing and maintaining the differential expression of a single X-linked gene, the hypoxanthine phosphribosyltransferase (HPRT) gene, on the active and inactive X chromosomes. We postulate that transcriptional regulation of the HPRT gene by X inactivation will involve a complex hierarchy of inter- dependent regulatory mechanisms, from long-range effects of higher order chromatin structure, to local nucleosome structure within the promoter and other regulatory regions, to individual sequence-specific DNA-protein interactions, each of which is crucial to the establishment and maintenance of differential expression of the HPRT gene on the active and inactive X chromosomes. We further postulate that the process of X chromosome inactivation will function through this hierarchy of mechanisms that regulate transcription of individual genes on the X chromosome. Thus, we will undertake a detailed study of the full range of mechanisms that influence HPRT gene transcription. The experiments proposed in this application will investigate two aspects of regulation of the HPRT gene by X chromosome inactivation. First, we will continue our detailed analysis of the HPRT promoter region on the active and inactive X chromosomes, and the effects of DNA methylation, local chromatin structure, and sequence- specific DNA-protein interactions on promoter function. Secondly, we will begin a long-term investigation of the structure and role of the HPRT chromatin domain in regulating expression of the HPRT gene on the active and inactive X chromosomes. This will involve defining the borders of the domain, then identifying and characterizing elements within the domain that regulate its chromatin structure. Understanding the mechanisms that regulate transcription of an individual X-linked gene by X inactivation should provide insights and experimental approaches to investigate the chromosomal and developmental aspects of this unique genetic process.