Molecular mechanisms of myogenesis

我们研究了肌发生的分子机制，它包括一系列过程，包括肌细胞谱系的确定、分化的诱导、肌肉特异性蛋白基因的表达和收缩结构的形成。结果表明：(1)激活素作为最有效的中胚层诱导因子，对爪蟾胚胎特定区域的外胚层和中胚层组织具有剂量依赖性。分析了Myf5的表达调控，Myf5是一种肌分化因子。(2)通过基因靶向法制备肌原素敲除小鼠。在小鼠中，生成了成肌细胞，但没有形成成熟的肌细胞，这表明肌生成素对肌生成的后期阶段至关重要。(3)发现了5个肌动蛋白基因簇，并分析了它们的表达特性。(4) c-Jun、Cdk2-cyclin A、Cdc2-cyclin B和Rb的表达和激活在SV40大T抗原诱导的肌肉细胞分化和去分化过程中起重要作用。(5)将小鼠骨骼肌细胞系C2注射到小鼠体内分化，建立了该系统。(6)克隆了参与肌肉形成过程中肌肉蛋白组装调控的profilin、115kDa α - actitin和cardiac C-protein的cdna，并确定了它们的初级序列。Cofilin是一种肌动蛋白调节蛋白，在肌肉变性过程中高度表达。用生物素偶联肌动蛋白电镜分析了肌动蛋白组装成心肌肌原纤维的过程。

We have studied on the molecular mechanisms of myogenesis, which consists of series of processes inculding the determination of myogenic cell linages, differentiation induction, expression of muscle-specific protein genes, and formation of contractile structures. The results are summarized as follows : (1) Activin, the most potent mesoderm-inducing factor, dose-dependently induced ectoderm and mesoderm tissues at particular areas of Xenopus embryos. Regulation of the espression of Myf5, a myogenic differentiation factor, was analyzed. (2) Myogenin-knock out mice were produced by gene targetting. In the mice, myoblasts were generated, but mature myocytes were not formed, indicating that myogenin is essential for late stages of muyogenesis. (3) Five clusters of muscle actin genes were discovered, and their expression properties were analyzed. (4) The expression and activation of c-Jun, Cdk2-cyclin A, Cdc2-cyclin B, and Rb play important roles in muscle cell differentiation and dedifferentiation induced by SV40 large T antigen. (5) The system was developed that the mouse skeletal muscle cell line C2 injected into mice defferentiated in vivo. (6) cDNAs were cloned and their primary sequences were determined of profilin, 115kDa alpha-actinin, and cardiac C-protein, which are involved in the regulation of muscle protein assembly during myogenesis. Cofilin, an actin-regulatory protein, was highly expressed during muscle degeneration. The process of actin assembly into cardiac muscle myofibrils was analyzed by electron microscopy using biotin-conjugated actin.