Investigating potential functions of nuclear and cytoplasmic condensation of the SMN complex in RNP homeostasis

大分子复合物完成广泛的细胞任务。它们由不同的蛋白质或蛋白质和核酸组成，它们的忠实组装通常需要反式作用因子的帮助。剪接体UsnRNP代表了一组充分研究的丰富的大分子复合物，在体内进行辅助组装。它们在SMN复合物的指导下形成，SMN复合物本身构成在核和细胞质无膜区室中可逆地凝聚的大分子实体。虽然我们理解的SMN-复合物在U snRNP在生化水平的核心功能，其空间和时间的调节，其在细胞UsnRNP稳态的潜在作用和其冷凝的功能意义仍然知之甚少。在本申请中，我们建议调查相分离的SMN复合物在响应细胞信号传导及其对UsnRNP稳态的影响，并作为生物合成途径的调节剂。在第一部分中，提出了实验，专注于核SMN复合物的作用。我们将测试的假设，核SMN复合物，凝聚在卡哈尔机构，作为周转中心，在细胞UsnRNP的稳态水平和/或有缺陷的UsnRNP的去除进行调节。在第二部分中，我们将利用以前确定的信号线索，管理SMN缩合物，以评估细胞质SMN缩合物的功能，以调节U snRNP组件在压力条件下，但也在新的功能的SMN复杂的翻译控制。我们的研究不仅将揭示SMN复合物的生物合成功能如何整合到细胞信号传导和应激反应中，还将深入了解相分离如何实现和调节SMN复合物的新功能。

Macromolecular complexes accomplish a wide spectrum of cellular tasks. Being composed of different proteins or proteins and nucleic acids, their faithful assembly often requires assistance by trans-acting factors. Spliceosomal UsnRNPs represent a well-studied group of abundant macromolecular complexes that undergo assisted assembly in vivo. They form under the guidance of the SMN-complex, which itself constitutes a macromolecular entity that reversibly condenses in nuclear and cytoplasmatic membraneless compartments. While we comprehend core functions of the SMN-complex in U snRNP at biochemical level, its spatial and temporal regulation, its potential roles in cellular UsnRNP homeostasis and the functional significance of its condensation remain only poorly understood. In this application we propose to investigate phase separation of the SMN complex in response to cellular signaling and its impact for UsnRNP homeostasis and as a regulator for biosynthetic pathways. In the first part, experiments are proposed that focus on the role of the nuclear SMN-complex. We will test the hypothesis that nuclear SMN-complexes, condensing in Cajal bodies, serve as turnover centers, where the steady state level of cellular UsnRNP and/or the removal of defective UsnRNPs are regulated. In the second part, we will exploit previously identified signaling cues that govern SMN condensation to evaluate the function of cytoplasmic SMN condensates to regulate U snRNP assembly under stress conditions but also in novel functions of the SMN complex in translational control. Our studies will not only unravel how the biosynthetic functions of the SMN complex are integrated into cell signaling and stress response but provide insight into how phase separation enables and regulates novel functions of the SMN complex.