Farrell E R, Fernandes J, Keshishian H
Biology Department, Yale University, New Haven, Connecticut 06520, USA.
Dev Biol. 1996 Jun 15;176(2):220-9. doi: 10.1006/dbio.1996.0129.
In many organisms muscle formation depends on specialized cells that prefigure the pattern of the musculature and serve as templates for myoblast organization and fusion. These include muscle pioneers in insects and muscle organizing cells in leech. In Drosophila, muscle founder cells have been proposed to play a similar role in organizing larval muscle development during embryogenesis. During metamorphosis in Drosophila, following histolysis of most of the larval musculature, there is a second round of myogenesis that gives rise to the adult muscles. It is not known whether muscle founder cells organize the development of these muscles. However, in the thorax specific larval muscle fibers do not histolyze at the onset of metamorphosis, but instead serve as templates for the formation of a subset of adult muscles, the dorsal longitudinal flight muscles (DLMs). Because these persistent larval muscle fibers appear to be functioning in many respects like muscle founder cells, we investigated whether they were necessary for DLM development by using a microbeam laser to ablate them singly and in combination. We found that, in the absence of the larval muscle fibers, DLMs nonetheless develop. Our results show that the persistent larval muscle fibers are not required to initiate myoblast fusion, to determine DLM identity, to locate the DLMs in the thorax, or to specify the total DLM fiber volume. However, they are required to regulate the number of DLM fibers generated. Thus, while the persistent larval muscle fibers are not obligatory for DLM fiber formation and differentiation, they are necessary to ensure the development of the correct number of fibers.
在许多生物体中，肌肉形成依赖于特定的细胞，这些细胞预先确定肌肉组织的模式，并作为成肌细胞组织和融合的模板。其中包括昆虫中的肌肉先驱细胞和水蛭中的肌肉组织细胞。在果蝇中，有人提出肌肉奠基细胞在胚胎发育期间组织幼虫肌肉发育中发挥类似作用。在果蝇变态发育过程中，大部分幼虫肌肉组织发生组织溶解后，会有第二轮肌生成，形成成虫肌肉。目前尚不清楚肌肉奠基细胞是否组织这些肌肉的发育。然而，在胸部，特定的幼虫肌肉纤维在变态发育开始时不会发生组织溶解，而是作为成虫肌肉的一个子集——背纵飞行肌（DLM）形成的模板。由于这些持续存在的幼虫肌肉纤维在许多方面似乎起着肌肉奠基细胞的作用，我们通过使用微束激光单独或联合消融它们，研究它们对于DLM发育是否必要。我们发现，在没有幼虫肌肉纤维的情况下，DLM仍然会发育。我们的结果表明，持续存在的幼虫肌肉纤维对于启动成肌细胞融合、确定DLM身份、在胸部定位DLM或确定DLM纤维总体积并非必需。然而，它们对于调节所产生的DLM纤维数量是必需的。因此，虽然持续存在的幼虫肌肉纤维对于DLM纤维的形成和分化不是必需的，但它们对于确保发育出正确数量的纤维是必要的。
