NUCLEAR & CHROMATIN PACKAGING OF MAMMALIAN X CHROMOSOME

描述（改编自研究者摘要）：哺乳动物X 染色体构成了一个重要的生物学和临床模型，用于控制 基因组功能通过形成兼性异染色质，一种现象 对正常发育至关重要，在癌症中被废除。印记XIST基因 是X失活所必需的，但不编码蛋白质。这个项目 研究了序列特异性相互作用的综合假设 XIST RNA和染色体之间的相互作用引发了染色质重塑的级联反应 在适当的细胞环境中，将活动的X 染色体形成高度浓缩的转录惰性巴尔体。的 研究人员已经证明，稳定的XIST转录本的积累 在结构上与X染色体相关联，基本上是“画”的 顺式染色体其他证据支持XIST RNA可以诱导启动 在正常发育过程中的染色质失活。一个中心问题 现在变成了：如何绘画XIST成绩单导致席卷 整个染色体的浓缩和抑制？这里的关键问题将是 生物化学和结构的相互关系 所涉及的变化，特别是XIST的作用，当表达在 在重排的染色体中，或作为常染色体转基因， 在正常发育环境之外诱发的。研究人员的创新 结合精确的分子和生物化学信息的分析方法 直接在染色体结构的背景下是重要的， XIST RNA对染色体影响。 每个目标都涉及几个具体的假设，作为每个更广泛的假设的一部分。 假设如下：1）XIST RNA本身不直接 抑制转录，但在发育能力细胞中触发 染色体沉默所需的后续变化。2)XIST RNA具有 对常染色体染色质的亲和力受损，导致不完全和 不稳定的常染色体失活。3)XIST RNA的物理作用 染色体依赖于染色体DNA和染色体中的特定序列。 XIST成绩单。4)间期染色体区域内的DNA 表现出更高层次的组织，这在Xi和Xa上不同，并且可能是 直接用XIST RNA治疗。在提出的新研究中， 协同生物信息学搜索基因组序列基序与高 对XIST的亲和力，以及诱导型转基因系统的产生，其中 XIST表达式可以很容易地操作，以定义其在 启动灭活。

DESCRIPTION (Adapted from the Investigator's Abstract): The mammalian X chromosome constitutes a vital biological and clinical model for control of genomic function through formation of facultative heterochromatin, a phenomenon central to normal development and abrogated in cancer. The imprinted XIST gene is required for X inactivation but does not encode a protein. This project investigates the comprehensive hypothesis that sequence-specific interactions between XIST RNA and the chromosome trigger a cascade of chromatin remodeling events that, in the appropriate cellular context, transform an active X chromosome into a highly condensed, transcriptionally inert Barr body. The investigators have shown that an accumulation of stable XIST transcripts structurally associates with the X chromosome, essentially "painting" the chromosome in cis. Other evidence supports that XIST RNA can induce initiation of chromatin inactivation in the normal developmental context. A central issue now becomes: how does painting by XIST transcripts lead to the sweeping condensation and repression of a whole chromosome? Here key questions will be addressed concerning the interrelationship of biochemical and structural changes involved, and the role of XIST in particular, when expressed either in its native context, in rearranged chromosomes, or as an autosomal transgene induced outside normal developmental context. The investigators' innovative analytical approach which couples precise molecular and biochemical information directly in the context of chromosome structure is important for revealing the impact that XIST RNA has on the chromosome. Each aim addresses several specific hypotheses as part of each broader hypothesis, which are as follows: 1) That XIST RNA does not itself directly repress transcription, but in developmentally competent cells triggers subsequent changes required for chromosome silencing. 2) That XIST RNA has compromised affinity for autosomal chromatin which results in incomplete and unstable autosomal inactivation. 3) That XIST RNA's physical interaction with the chromosome depends upon specific sequences both in chromosomal DNA and in the XIST transcript. 4) That DNA within an interphase chromosome territory exhibits higher-order organization, which differs on Xi and Xa, and may be medicated directly by XIST RNA. Among the novel studies proposed is a collaborative bioinformatics search for genomic sequence motifs with high affinity for XIST, and the production of an inducible transgene system in which XIST expression can be easily manipulated to define its precise role in initiating inactivation.