Regulation of actin dynamics during myofibril assembly

描述（由申请人提供）：横纹肌中的肌节是收缩器官的基本单位。有组织的肌节结构的组装和维持对于产生收缩力是必不可少的。肌动蛋白是肌节细丝的主要成分之一，在横纹肌中，细丝的长度和方向受到精确的调节。然而，肌节肌动蛋白丝的组装和维持机制是复杂的，知之甚少。更令人困惑的是，微丝内的肌动蛋白亚基是动态交换的，而不会损害整体结构和收缩功能。已经在骨骼肌中鉴定了许多肌动蛋白动力学的调节剂，其中一些与遗传性肌肉疾病有关。特别是，线虫性肌病涉及骨骼肌中异常的富含肌动蛋白的聚集体或杆的形成，并且是由肌动蛋白或肌动蛋白动力学的调节剂（包括星云蛋白、原肌球蛋白和cofilin）的突变引起的。因此，肌动蛋白动力学的调节对于在骨骼肌中建立功能性收缩装置是至关重要的，并且该系统的功能障碍导致肌肉疾病。为了研究横纹肌肌动蛋白动力学的调控机制，我们一直使用线虫线虫作为模型系统。C. elegans是横纹肌，肌节蛋白在C. elegans优雅and humans人类.对这些肌肉蛋白质的强有力的遗传学研究推进了我们对肌原纤维组装和功能机制的认识。使用这个系统，我们已经确定，ADF/cofilin和AIP 1提高营业额的肌动蛋白丝和肌节肌动蛋白丝的有组织的装配必不可少的，和原肌球蛋白和钙调蛋白样蛋白拮抗ADF/cofilin和稳定肌节肌动蛋白丝。这些发现使我们假设，肌动蛋白动力学的增强子和抑制子之间的平衡是至关重要的肌节组装和维护。最近，我们获得的证据表明，其他调节肌动蛋白动力学参与肌节肌动蛋白的调节。因此，我们提出了三个具体的目标，以进一步研究它们在肌原纤维组装中的作用：（目的1）我们鉴定了一种在体壁肌肉中富集的环化酶相关蛋白异构体，并将确定环化酶相关蛋白如何与ADF/cofilin和AIP 1合作调节肌动蛋白更新，（目的2）我们鉴定了一种具有强肌动蛋白切割活性的凝溶胶蛋白样蛋白， 在体壁肌肉中富集，并将研究其在肌动蛋白组织中的作用，以及（目的3）我们证明了肌动蛋白调节蛋白在肌节细丝尖端附近的独特定位模式，并将研究肌动蛋白动力学如何在这个专门的区域进行调节。我们希望这项研究的结果将提供新的见解横纹肌肌动蛋白动力学的调节。

DESCRIPTION (provided by applicant): Sarcomere in striate muscle is the basic unit of contractile apparatuses. Assembly and maintenance of organized sarcomeric structure are essential for producing contractile forces. Actin is one of the major components of sarcomeric thin filaments, and length and orientation of the filaments are precisely regulated in striated muscle. However, the mechanism of assembly and maintenance of sarcomeric actin filaments is complex and poorly understood. What is more puzzling is that actin subunits within thin filaments are dynamically exchanged without compromising overall structure and contractile functions. A number of regulators of actin dynamics have been identified in skeletal muscle, and some of them are linked to genetic muscle disorders. In particular, nemaline myopathy involves formation of abnormal actin-rich aggregates or rods in skeletal muscle and is caused by mutations in actin or regulators of actin dynamics including nebulin, tropomyosin, and cofilin. Therefore, the regulation of actin dynamics is fundamentally important for building functional contractile apparatuses in skeletal muscle, and malfunction in this system leads to muscle disorders. To investigate the regulatory mechanism of actin dynamics in striated muscle, we have been using the nematode Caenorhabditis elegans as a model system. Body wall muscle of C. elegans is striated muscle, and most of sarcomeric proteins are conserved between C. elegans and humans. Powerful genetic studies on these muscle proteins advanced our knowledge on the mechanism of myofibril assembly and function. Using this system, we have identified that ADF/cofilin and AIP1 enhance turnover of actin filaments and essential for organized assembly of sarcomeric actin filaments, and that tropomyosin and calponin-like protein antagonize ADF/cofilin and stabilize sarcomeric actin filaments. These findings led us to hypothesize that a balance between enhancers and suppressors of actin dynamics is crucial for sarcomere assembly and maintenance. Recently, we obtained evidence that additional regulators of actin dynamics are involved in sarcomeric actin regulation. Therefore, we propose to further investigate their roles in myofibril assembly in three specific aims: (Aim 1) We identified a cyclase-associated protein isoform that is enriched in body wall muscle and will determine how cyclase-associated protein cooperate with ADF/cofilin and AIP1 to regulate actin turnover, (Aim 2) We identified a gelsolin-like protein with strong actin-severing activity that is enriched in body wall muscle and will investigate its role in actin organization, and (Aim 3) We demonstrated distinct localization patterns of actin-regulatory proteins near the pointed ends of sarcomeric thin filaments and will investigate how actin dynamics are regulated in this specialized region. We expect that results of this research will provide new insight into the regulation of actin dynamics in striated muscle.