Regulation of actin dynamics during myofibril assembly

描述（由申请人提供）：肌动蛋白细胞骨架适应于许多不同的结构，并参与多种细胞功能。细胞骨架结构的分化通常由一些肌动蛋白结合蛋白控制，这些蛋白调节肌动蛋白丝的动力学和组织。横纹肌中的肌原纤维是肌动蛋白细胞骨架的高度分化形式，专门用于产生收缩力。然而，肌动蛋白丝在发育过程中组装成肌原纤维并在收缩装置中维持的机制在很大程度上是未知的。秀丽隐杆线虫体壁有斜横纹肌，它与脊椎动物的横纹肌在生化和功能上有许多相似之处。我们已经确定肌动蛋白解聚因子(ADF)/cofilin，肌动蛋白相互作用蛋白1 （AIP1）和原肌球蛋白是肌动蛋白组织在体壁肌肉中的关键调节因子。当这些蛋白有缺陷时，肌动蛋白丝紊乱，体壁肌的收缩性受损。此外，我们获得的证据表明，钙钙蛋白样蛋白UNC-87和免疫球蛋白样重复蛋白kettin可能稳定肌动蛋白丝，而肌肉特异性谱蛋白PFN-3可能有助于肌动蛋白单体的再循环用于聚合。尽管对这些蛋白的遗传和生化分析表明，这些肌动蛋白结合蛋白中的每一种都可能对肌动蛋白动力学的调节很重要，但我们不了解这些蛋白是如何在功能上相互作用的。我们假设ADF/cofilin是肌动蛋白动力学的关键增强因子，并在功能上与其他肌动蛋白结合蛋白相互作用，以调节肌动蛋白在横纹肌原纤维组装和维持过程中的聚合、解聚和稳定性。在这个项目中，我们的目标是研究秀丽隐杆线虫肌肉细胞中肌动蛋白动力学的三个方面的机制：（目的1）确定ADF/cofilin和AIP1如何分解肌动蛋白丝；（目的2）确定肌动蛋白单体如何在肌肉细胞中回收聚合；（目的3）确定肌动蛋白丝如何在肌肉细胞中稳定。这些研究不仅为肌动蛋白正常组装和维持的机制提供了重要的信息，而且还为线状肌病的发病机制提供了重要的信息，其中肌动蛋白丝稳定性的失调涉及到线状肌病。

DESCRIPTION (provided by applicant): The actin cytoskeleton is adapted to many different structures and involved in diverse cellular functions. Differentiation of the cytoskeletal structures is generally controlled by a number of actin-binding proteins that regulate dynamics and organization of the actin filaments. Myofibrils in striated muscle are highly differentiated forms of the actin cytoskeleton and specialized for generating contractile forces. However, the mechanisms by which actin filaments are assembled into myofibrils during development and maintained in the contractile apparatuses are largely unknown. The nematode Caenorhabditis elegans has obliquely striated muscle in the body wall, which shares a number of biochemical and functional similarities with vertebrate striated muscle. We have identified actin depolymerizing factor (ADF)/cofilin, actin-interacting protein 1 (AIP1), and tropomyosin as key regulators of actin organization in the body wall muscle. When these proteins are defective, the actin filaments are disorganized and the contractility of the body wall muscle is impaired. In addition, we obtained evidence that UNC-87, a calponin-like protein, and kettin, immunoglobulin-like repeat protein, may stabilize actin filaments, and PFN-3, a muscle-specific profilin, may help recycling actin monomers for polymerization. Although genetic and biochemical analyses of these proteins suggest that each of these actin-binding proteins might be important for regulation of actin dynamics in muscle cells, we do not understand how these proteins functionally interact. We hypothesize that ADF/cofilin is a key enhancer of actin dynamics and functionally interacts with other actin-binding proteins to regulate actin polymerization, depolymerization, and stability during assembly and maintenance of the striated myofibrils. In this project, we aim to investigate mechanisms of three aspects of actin dynamics in muscle cells in C. elegans: (Aim 1) To determine how ADF/cofilin and AIP1 disassemble actin filaments in muscle cells, (Aim 2) To determine how actin monomers are recycled for polymerization in muscle cells, and (Aim 3) To determine how actin filaments are stabilized in muscle cells. These studies should provide important information not only on the mechanism of normal myofibril assembly and maintenance but also on the pathogenesis of nemaline myopathy in which misregulation of actin filament stability is implicated.