Cossu G, Tajbakhsh S, Buckingham M
Institute of Histology and General Embryology, University of Rome La Sapienza, Italy.
Trends Genet. 1996 Jun;12(6):218-23. doi: 10.1016/0168-9525(96)10025-1.
Skeletal myoblasts are derived from paraxial mesoderm, but how myoblasts acquire their identity is still a matter of speculation. The characterization of molecular markers and, in some cases, the analysis of mutations in the corresponding genes, has now made it possible to ask specific questions about this process. Specification of somite cell fate depends on epigenetic factors. Adjacent tissues, such as the neural tube, notochord, dorsal ectoderm and lateral mesoderm, act either positively or negatively on the different myogenic precursor populations in the somite. Candidate molecules for this complex signalling activity include sonic hedgehog and the Wnt proteins as positive signals, and BMP4 as a possible inhibitor. Although it is generally assumed that induction is required, some observations suggest that embryonic cells might have a tendency to undergo myogenesis as a 'default' pathway. By analogy with Drosophila, where the neurogenic genes affect myogenesis, the vertebrate homologues of notch and its ligands could be candidate molecules for a repression or derepression mechanism. Similar studies with cultured muscle cells also implicate other HLH factors as potential inhibitors of the MyoD family and, hence, of inappropriate myogenesis.
骨骼肌成肌细胞起源于轴旁中胚层，但成肌细胞如何获得其特性仍是一个推测的问题。分子标志物的特征鉴定，以及在某些情况下对相应基因突变的分析，现在使得能够就这一过程提出具体问题。体节细胞命运的特化取决于表观遗传因素。相邻组织，如神经管、脊索、背侧外胚层和外侧中胚层，对体节中不同的成肌前体群体起正向或负向作用。这种复杂信号活动的候选分子包括作为正向信号的音猬因子和Wnt蛋白，以及作为可能抑制剂的骨形态发生蛋白4。尽管通常认为需要诱导，但一些观察结果表明，胚胎细胞可能有一种作为“默认”途径进行肌生成的倾向。与果蝇类似，果蝇中的神经发生基因影响肌生成，Notch及其配体的脊椎动物同源物可能是抑制或去抑制机制的候选分子。对培养的肌肉细胞进行的类似研究也表明，其他HLH因子可能是MyoD家族的潜在抑制剂，因此也是不适当肌生成的潜在抑制剂。
