Methylation of Sm proteins - Roles in snRNP Biogenesis and germline specification

描述（由申请人提供）：Sm类小核核糖核蛋白（snRNP）是剪接体的核心组分，是体内剪接所需的。此外，Sm蛋白似乎有一个更古老的作用，在规范的种系。该项目的总体目标是了解Sm蛋白组装成snRNP的机制，以剪接或组装成建立生殖细胞命运所需的专门的核糖核蛋白（RNP）。在这两个看似不同的途径的连接处是PRMT5复合体。snRNP的生物发生是高度协调的，需要几个重要的辅因子。特别是，细胞质snRNP组装依赖于两个异聚体复合物，PRMT5复合物和SMN复合物。重要的是，降低SMN蛋白水平的突变与称为脊髓性肌萎缩症（SMA）的神经退行性疾病相关。患有这种疾病的患者往往在儿童时期很早就死亡。SMA的分子病因学尚不清楚，然而，snRNP生物发生的干扰被认为是主要的促成因素。对snRNP组装机制的详细了解将有助于了解疾病过程。PRMT5复合物负责对称二甲基化Sm蛋白，并且凭借这种活性，被认为与SMN复合物合作介导有效的snRNP组装。然而，目前缺乏对这一过程的体内检查。此外，PRMT5与BLIMP1相关，是小鼠生殖细胞发育所需的。因此，破坏PRMT5活性可能会影响两个不同但可分离的途径-snRNP生物发生和生殖细胞发育。为了深入了解这些过程的机理，我们已经开发了利用果蝇作为模型系统以及哺乳动物细胞培养技术的体内方案。目的1探讨snRNP生物发生中Sm蛋白甲基化的必要性。由于SMN与甲基化Sm蛋白的结合亲和力更高，因此这种修饰可以作为SMA表型的修饰剂。具体而言，哺乳动物中Sm蛋白甲基化的缺乏可能表型SMA。或者，增加甲基化可以改善疾病的严重程度。目的2检查DartS的要求，飞直系同源的PRMT5，在生殖细胞规格和地址的特定作用，Sm蛋白在这个过程中发挥。摘要：脊髓性肌萎缩症是一种常见的遗传性疾病，导致儿童早期死亡。虽然已经确定了导致疾病的基因，但最终导致疾病病理学的机制尚不清楚。为了开发有效的治疗方法，对疾病基因产物的分子理解是必不可少的。

DESCRIPTION (provided by applicant): Sm class small nuclear ribonucleoproteins (snRNPs) are core components of the spliceosome and are required for splicing in vivo. In addition, Sm proteins appear to have a more ancestral role in specification of the germline. The overall goal of this project is to understand the mechanism by which Sm proteins are assembled into snRNPs for the purpose of splicing or into specialized ribonucleoproteins (RNPs) required to establish germ cell fate. At the nexus of these two seemingly disparate pathways is the PRMT5 complex. The biogenesis of snRNPs is highly orchestrated, requiring several essential co-factors. In particular, cytoplasmic snRNP assembly relies on two heteromeric complexes, the PRMT5 complex and the SMN complex. Importantly, mutations that reduce the level of SMN protein are correlated with a neurodegenerative disease known as Spinal Muscular Atrophy (SMA). Patients with the disease often die very early in childhood. The molecular etiology of SMA is unknown, however, perturbation of snRNP biogenesis is thought to be a major contributing factor. A detailed understanding of the mechanism of snRNP assembly will shed light on the disease process. The PRMT5 complex is responsible for symmetrically dimethylating Sm proteins, and by virtue of this activity, is thought to cooperate with the SMN complex in mediating efficient snRNP assembly. However, an in vivo examination of this process is currently lacking. Furthermore, PRMT5 associates with BLIMP1 and is required for germ cell development in the mouse. Disruption of PRMT5 activity could thus impinge on two distinct but separable pathways - snRNP biogenesis and germ cell development. To gain mechanistic insight into these processes we have developed in vivo protocols making use of Drosophila as a model system as well as mammalian cell culture techniques. Aim 1 explores the requirement for Sm protein methylation in snRNP biogenesis. Since SMN binds with a higher affinity to methylated Sm proteins, this modification may act as a modifier of the SMA phenotype. Specifically, lack of Sm protein methylation in mammals may phenocopy SMA. Alternatively, increased methylation may ameliorate the disease severity. Aim 2 examines the requirement for DartS, the fly ortholog of PRMT5, in germ cell specification and addresses the specific role played by Sm proteins in this process. Lay summary: Spinal Muscular Atrophy, a common genetic disease, results in very early childhood mortality. Whereas the gene responsible for the disease has been identified, the mechanism that ultimately results in the disease pathology is unknown. In order to develop effective therapies, a molecular understanding of the disease gene product is essential.