Dissecting the role of U5 snRNA isoforms as drivers of U5 snRNP diversity and spliceosome plasticity during development and homeostasis

前-信使核糖核酸剪接是后生动物基因表达调控的关键一步，对组织和器官发育、动态平衡和生物体健康具有关键作用。剪接体催化的“剪切和连接”过程必须是高效和精确的，但也必须灵活，以根据需要生成特定的转录本。相比之下，剪接体成分的突变和放松调控是导致许多人类疾病和生物衰老的原因。产生不同细胞类型特异性剪接模式的能力与剪接体的动态组成有关。剪接体由5个小核核糖核蛋白颗粒组成，每个小核糖核蛋白颗粒都含有特定的富含尿苷的小核糖核酸，以及一组核心和辅助蛋白。有趣的是，高等真核生物与酵母不同，它们编码几种不同的U单链RNA亚型，显示出特定的时空表达。它们在动态剪接体结构和功能可塑性中的作用和贡献在很大程度上尚不清楚。我们的工作，使用了遗传上易驯化的果蝇模型，为调控剪接体的生物发生、功能和调控的机制提供了新的见解(Claudius等人，2015，Erkelenz等人，2021)。此外，我们还证明了它与核心剪接因子Prp8突变引起的退行性眼病视网膜色素变性的病因学和病理学研究的相关性(Stankovic等人，2020年)。在这里，我们建议在果蝇模型中结合功能遗传学、基因组学和蛋白质组学方法，揭示果蝇基因组中编码的七种U5单链RNA亚型在组织和发育阶段的特定要求。我们将确定单个U5 SnRNA异构体在塑造U5 SnRNP组成中的作用，以及它们对建立发育阶段和组织特异性剪接程序的贡献。最后，我们将定义U5 SnRNA·RNA碱基配对相互作用的体内功能，作为剪接位点选择和维持转录组完整性的晚期检查点机制的一部分。我们相信，我们的工作将对基础和生物医学研究具有普遍重要性，促进对后生动物中规范和替代前mRNA剪接的机制的理解。

Pre-mRNA splicing represents a crucial step in the regulation of gene expression in metazoans pivotal to tissue and organ development, homeostasis, and organismal healthspan. The “cut and join” process catalyzed by a spliceosome must be efficient and precise but also flexible to generate specific transcripts on demand. In contrast, mutations in, and deregulation of, spliceosome components underlie numerous human diseases and organismal aging. The capacity to generate diverse cell-type-specific splicing patterns has been linked to the dynamic composition of the spliceosome. The spliceosome consists of five small nuclear ribonucleoprotein particles (snRNPs) each comprising of specific uridine-rich small nuclear RNA (U snRNA), and a set of core and accessory proteins. Intriguingly, higher eukaryotes, unlike yeast, encode several isoforms of individual U snRNAs, which show specific spatiotemporal expression. Their roles and contribution to the dynamic spliceosome architecture and functional plasticity remain largely unknown. Our work, using the genetically tractable Drosophila model, has provided novel insights into mechanisms governing spliceosome biogenesis, function, and regulation (Claudius et al., 2015, Erkelenz et al., 2021). Moreover, we have demonstrated its relevance for mechanistic studies of etiology and pathology of a degenerative eye disorder retinitis pigmentosa caused by mutations in the core splicing factor Prp8 (Stankovic et al., 2020). Here we propose to combine functional genetics, genomic and proteomic approaches in the Drosophila model to unravel the tissue- and developmental-stage specific requirements for the seven U5 snRNA isoforms encoded in the fly genome. We will determine the role of the individual U5 snRNA isoforms in shaping the U5 snRNP composition and their contribution to establishing the developmental stage- and tissue-specific splicing programs. Finally, we will define the in vivo function of the U5 snRNA• RNA base-pairing interactions as a part of the late checkpoint mechanism for splice site selection and the maintenance of transcriptome integrity. We believe that our work will be of general importance for basic and biomedical research, advancing the understanding of mechanisms that control canonical and alternative pre-mRNA splicing in metazoans.