Molecular Mechanisms of Myoblast Fusion

描述(申请人提供)：骨骼肌是一种独特的器官，由多核肌纤维组成，每一种肌纤维都是数百甚至数千个成肌细胞融合的产物。成肌细胞融合不仅对骨骼肌发育非常重要，而且对基于卫星细胞的肌肉再生也是至关重要的。尽管经过了几十年的大量研究，但人类成肌细胞融合的机制仍然知之甚少。最近对果蝇的研究已经开始揭示成肌细胞融合的分子和细胞机制的前所未有的细节。果蝇和哺乳动物肌肉发生之间显著的进化保守性使果蝇成为研究体内成肌细胞融合的一个特别相关的系统。我们实验室最近的研究揭示了成肌细胞融合的一种新的细胞机制。我们发现成肌细胞的融合是由一种细胞类型特异的富含F-肌动蛋白的足体样结构(PLS)介导的，该结构通过多个伸出的手指入侵相对的融合伙伴，导致融合孔的形成。为了进一步研究侵袭性最低密度脂蛋白的调控，这是介导成肌细胞融合的关键细胞结构，我们建议研究两个新基因DPak3和Dynamin的分子和细胞功能，这两个基因以前都与人类疾病有关。我们将运用遗传学、细胞生物学和生物化学等多方面的方法，研究Dpak3和Dynamin在果蝇成肌细胞融合过程中调控肌动蛋白聚合动力学的机制。我们还将研究它们的哺乳动物同源基因在小鼠C2C12成肌细胞融合中的作用。鉴于果蝇和哺乳动物之间成肌细胞融合在分子和细胞上的保守性，利用更简单和遗传上易于处理的果蝇系统进行的机制研究将对人类肌肉生物学在健康和疾病方面产生重要的见解，并最终为开发更有效的治疗削弱生命的肌肉退行性疾病的药物提供基础。

DESCRIPTION (provided by applicant): Skeletal muscle is a unique organ that is composed of multinucleate muscle fibers, each of which is the product of fusion of hundreds or even thousands of myoblasts. Myoblast fusion is not only important for skeletal muscle development, but also critical for satellite cell-based muscle regeneration. Despite a large body of studies ove several decades, the mechanisms underlying myoblast fusion in humans remain poorly understood. Recent studies in the fruit fly Drosophila have begun to reveal unprecedented details about the molecular and cellular mechanisms of myoblast fusion. The striking evolutionary conservation between fly and mammalian myogenesis makes Drosophila a particularly relevant system to study myoblast fusion in vivo. Recent studies from our lab have uncovered a novel cellular mechanism underlying myoblast fusion. We show that myoblast fusion is mediated by a cell type-specific, F-actin-enriched podosome-like structure (PLS), which invades the opposing fusion partner with multiple protrusive fingers leading to fusion pore formation. To further characterize the regulation of the invasive PLS, the key cellular structure mediating myoblast fusion, we propose to investigate the molecular and cellular functions of two new genes, DPak3 and dynamin, both have previously been implicated in human diseases. We will use a multifaceted approach, including genetics, cell biology and biochemistry, to study the mechanisms by which DPak3 and dynamin regulate actin polymerization dynamics within the PLS in Drosophila myoblast fusion. We will also investigate the function of their mammalian orthologs in the fusion of mouse C2C12 myoblasts. Given the molecular and cellular conservation of myoblast fusion between fly and mammals, the proposed mechanistic studies using the simpler and genetically tractable Drosophila system will lead to significant insights int human muscle biology in health and disease, and ultimately provide a basis for developing more efficient therapeutics against the life debilitating muscle degeneration diseases.