The Frizzled Nuclear Import Pathway in Synapse Development

描述（由申请人提供）：该项目的长期目标是了解突触发育的信号机制。利用果蝇幼虫神经肌肉连接处（NMJ）的强大策略，我们发现了一个非规范的Wnt信号通路，卷曲核输入（FNI）通路，这是正常突触发育所必需的。在上一个资助周期中，我们发现FNI通路与含有突触特异性mrna的大核糖核蛋白颗粒（megaRNPs）的形成和核出口有关。在这一途径中，内源性转录本被包装在细胞核内的megaRNP颗粒中，然后通过核膜出芽出口到细胞质，这一过程类似于疱疹型病毒的核出口。本应用程序中的方法构成了一种精辟的策略，以阐明这种新型核出口模式背后的分子机制。正如揭示核孔复合体的分子成分在理解转录、RNA加工和翻译的调控方面取得了重大进展一样，我们期望揭示核膜出芽的成分将为这些过程提供重要和新颖的视角。我们的研究确定了Torsin，一种aaa - atp酶，在人类中与早期发作的肌张力障碍有关，是萌芽所需的核膜重塑的关键因素。我们还发现细胞极性复合物的组成部分（非典型蛋白激酶C、Par3/Bazooka和Dap160/Intersectin）是核巨核np输出过程中核层局部重塑的重要决定因素。在这个项目中，我们提出了一个全面的策略来揭示萌芽机制的其他组成部分，并确定它们对突触发育和功能的影响。本项目的具体目的是：(1)确定核megaRNP通过核膜出芽输出的分子关键；(2)确定Torsin的功能作用并确定下游效应物；(3)验证Dap160、Baz和Par6调节aPKC依赖的核层局部重塑以实现megaRNP的核膜出芽的假设。通过对核膜相关营养不良症（如层状病变和包膜病变）、HSV型感染和肌张力障碍等疾病的机制基础提供新的见解，我们希望我们的研究能为治疗或治愈这些疾病的疗法设计打开新的窗口。

DESCRIPTION (provided by applicant): The long-term goal of this project is to understand the signaling mechanisms underlying synapse development. Using powerful strategies at the Drosophila larval neuromuscular junction (NMJ) we have uncovered a non-canonical Wnt signaling pathway, the Frizzled Nuclear Import (FNI) pathway, which is required for proper synapse development. During the last funding cycle, we found that the FNI pathway is associated with the formation and nuclear egress of large ribonucleoprotein granules (megaRNPs) containing synapse-specific mRNAs. In this pathway, endogenous transcripts are packaged in megaRNP granules within the nucleus and are then exported to the cytoplasm by budding through the nuclear membrane in a process akin to the nuclear egress of Herpes-type viruses. The approach in this application constitutes an incisive strategy to elucidate the molecular machinery underlying this novel mode of nuclear export. In the same manner by which uncovering molecular components of the nuclear pore complex has led to major progress in understanding regulation of transcription, RNA processing and translation, we expect that unraveling constituents of nuclear envelope budding will shed important and novel perspectives on these processes. Our studies identify Torsin, a AAA-ATPase, which in humans is linked to early onset dystonia as a key element in the remodeling of nuclear membranes required for budding. We have also identified components of the cell polarity complex (atypical Protein Kinase C, Par3/Bazooka and Dap160/Intersectin) as important determinants of local remodeling of the nuclear lamina during nuclear megaRNP egress. In this project we propose a comprehensive strategy to uncover other components of the budding machinery and to determine their impact on synapse development and function. The specific aims of this project are (1) to identify the molecular linchpins of nuclear megaRNP export by nuclear envelope budding, (2) to determine the functional role of Torsin and identify downstream effectors and (3) test the hypothesis that Dap160, Baz and Par6 regulate aPKC- dependent local remodeling of the nuclear lamina to enable nuclear envelope budding of megaRNPs. By providing novel insight into the mechanistic basis of such diseases as nuclear envelope-associated dystrophies (e.g., laminopathies and envelopathies), HSV- type infections and dystonia, we expect our studies to open new windows for the design of therapies to treat or cure these conditions.