The Control of Gene Expression by Eukaryotic Ribonucleases

描述(申请人提供)：RNA分子的降解为控制特定基因的表达提供了一种强有力的手段。真核细胞中主要的RNA降解途径之一是无义介导的mRNA衰变途径，它降解含有提前翻译终止密码子(PTCs)的RNA。虽然该途径在消除含有PTC的RNA中的功能已有很好的文献报道，但该途径在内源转录产物的表达调控和质量控制中的影响仍不清楚。拟议的项目将集中于NMD在特定基因调控途径中的三个主要功能。首先，我们将研究NMD如何与其他降解系统合作降解未剪接的前mRNAs，以及将这些未剪接RNA引导到不同的降解途径的机制。这一功能非常关键，因为未剪接的前mRNAs的积累将导致产生具有有害或显性负性的蛋白质。此外，我们还将研究NMD如何调节选择性剪接或调节转录本的产生。这将包括使用RNA-Seq方法对在包括PTC在内的可选剪接位点剪接的转录本进行基因组研究，并了解这些可选剪接事件是如何调节以响应环境变化的。我们还发现了NMD RNA解旋酶Upf1p在控制减数分裂过程中特异剪接或表达的转录本中的一个意想不到的功能，我们将研究Upf1p在这一过程中的具体作用。最后，我们发现NMD降解了位于亚端粒区域的许多基因的5‘-扩展形式，并且我们已经证明了这些扩展形式在真正的启动子处介导了转录的抑制。我们将研究这些RNA介导这些抑制功能的机制以及NMD在这个新的调控系统中的作用。总体而言，拟议的研究应该阐明NMD在基因表达调控中的主要影响，并揭示由这一独特的RNA质量控制途径控制的基因调控的新范例。 与公共卫生相关：导致遗传病的突变通常会导致过早翻译终止密码子，这反过来又通过无义介导的衰退调节由这些基因编码的mRNAs的快速降解。遗传病也可以由剪接信号的突变引起，剪接信号突变会降低剪接效率或激活隐蔽的剪接位点。我们对未剪接和错误剪接的RNA周转的研究将有助于揭示在大量遗传病的背景下，RNA降解控制突变基因表达的机制。

DESCRIPTION (provided by applicant): Degradation of RNA molecules provides a powerful means to control the expression of specific genes. One of the major RNA degradation pathways in eukaryotic cells is the Nonsense-Mediated mRNA decay pathway, which degrades RNA containing premature translation termination codons (PTCs). While the functions of this pathway in eliminating PTC-containing RNAs are well documented, the impact of this pathway in the regulation of expression and the quality control of endogenous transcripts is still unclear. The proposed project will focus on three major functions for NMD in specific gene regulation pathways. First, we will study how NMD can cooperate with other degradation systems to degrade unspliced pre-mRNAs, and the mechanisms that are involved to direct these unspliced RNAs to the different degradation routes. This function is highly critical since accumulation of unspliced pre-mRNAs would result in the production of proteins with deleterious or dominant-negative properties. In addition we will investigate how NMD can regulate the production of alternatively spliced or regulated transcripts. This will include the genomic investigation of transcripts that are spliced at alternative splice sites that include PTCs using RNA-Seq approaches, and understanding how these alternative splicing events are regulated to respond to environmental changes. We have also found an unexpected function for the NMD RNA helicase Upf1p in the control of transcripts specifically spliced or expressed during meiosis and we will investigate the specific role of Upf1p in this process. Finally we found that NMD degrades 5'-extended forms of many genes located within subtelomeric regions, and we have demonstrated that these extended forms mediate the repression of transcription at the bona fide promoters. We will investigate the mechanisms by which these RNAs mediate these repressive functions and the role of NMD in this novel regulatory system. Overall the proposed studies should illustrate the major impact of RNA degradation by NMD in the regulation of gene expression and reveal novel paradigms of gene regulation controlled by this unique RNA quality control pathway. PUBLIC HEALTH RELEVANCE: Mutations that cause genetic diseases often result in premature translation termination codons, which in turn mediate the rapid degradation of mRNAs encoded by these genes by Nonsense Mediated Decay. Genetic Diseases can also result from mutations in splicing signals, which reduce the splicing efficiency or activate cryptic splice sites. Our studies of the turnover of unspliced and mis-spliced RNAs will shed light on the mechanisms by which RNA degradation controls the expression of genes mutated in the context of a large number of genetic diseases.