MOLECULAR MECHANISMS OF CHROMOSOME CHOICE

描述（改编自研究者摘要）：本项目的目标是 以确定确定Xist mRNA稳定性的机制。基于先前 研究人员的工作，小鼠Xist基因的结构已经被 修改以包括基因3'端的新信息。研究者 已经表明该基因的这一区域比以前明显更大， 报道小鼠和人之间的序列比较揭示了序列 在新的3'端的相似性。使用北方分析和RNA酶 保护实验，研究人员已经证实，Xist mRNA 同种型通过包括差异多聚腺苷酸化的机制产生。 这些多聚腺苷酸化位点位于鉴定的新3'序列中。 另外的表达研究表明，Xist mRNA同种型是 发育调节，因此表现出不同的稳定性。这 表达模式表明调控元件可能相互作用， 不同的mRNA亚型，这反过来又可能影响Xist 在发育早期表达。数据表明Xist mRNA亚型 独立于Tsix的变化，Xist的发育调节 亚型受mRNA稳定的影响，在此期间， 观察到所选X染色体的上调。 负责Xist稳定性的具体机制仍然很差 表征了虽然Xist在开发初期并不稳定， 显影Xist异常稳定（T1/2 = >5小时）。最近的数据 在这一规定的Xist的5'端的重要性提出了疑问。的 研究人员计划探索Xist新的3'末端在基因中的作用。 稳定他还建议推行发展性监管机制 从两个方向看Xist稳定性。首先，一个完整的突变分析 Xist和紧邻Xist的区域将被完成。二是 研究人员计划评估甲基化途径中的基因， 它们在确定Xist mRNA稳定性中的作用。

DESCRIPTION (Adapted from investigator's abstract): The goal of this project is to define the mechanism that determines Xist mRNA stability. Based on previous work by the investigator, the structure of the murine Xist gene has been revised to include new information on the 3' end of the gene. The investigator has shown that this area of the gene is significantly larger than previously reported. Sequence comparison between mouse and human revealed sequence similarity in the new 3' ends. Using both Northern analysis and RNAse protection experiments, the investigator has confirmed that both Xist mRNA isoforms are produced by a mechanism involving differential polyadenylation. These polyadenylation sites are located in the new 3' sequences identified. Additional expression studies have shown that Xist mRNA isoforms are developmentally regulated, and therefore show different stabilities. This pattern of expression suggests that regulatory elements may interact differentially with each mRNA isoform, which in turn may influences Xist expression early in development. The data suggest that Xist mRNA isoforms change independently of Tsix and that the developmental regulation of the Xist isoforms is influenced by mRNA stabilization during the period in which upregulation of the chosen X chromosome is observed. The specific mechanism responsible for Xist stability remains poorly characterized. Although early in development Xist is unstable, after development Xist is exceptionally stable (T1/2 = >5 hr). Recent data have placed in doubt the importance of the 5' end of Xist in this regulation. The investigator plans to explore the role of the new 3' end of Xist in gene stability. He also proposes to pursue the mechanism of developmental regulation of Xist stability from two directions. First, a complete a mutational analysis of Xist and the regions immediately adjacent to Xist will be done. Second, the investigator plans to evaluate genes in the methylation pathway and define their role in determining Xist mRNA stability.