Deries Marianne, Collins Jennifer J P, Duxson Marilyn J
Department of Anatomy and Structural Biology, Otago School of Medical Sciences, University of Otago, PO Box 913, Dunedin, New Zealand.
Evol Dev. 2008 Nov-Dec;10(6):746-55. doi: 10.1111/j.1525-142X.2008.00289.x.
The segmented muscular myotome is the first muscle to form in all vertebrates. In fish and amphibian embryos, the myotome becomes innervated very early and is essential for larval swimming. Its role in birds and mammals, however, is not clear. Using immunohistochemistry on sections and whole mounts of rat embryos, we demonstrate that the mammalian myotome differentiates and develops over a period of 3 days without being invaded by the outgrowing spinal nerves. In contrast, the limb muscle masses become filled with fine nerve branches from the first time that myocyte differentiation can be detected. Additionally, we show that the mammalian myotome does not express clustered acetylcholine receptors until after embryonic day 13.5, which corresponds to the beginning of its transformation into the adult epaxial muscles, showing that there are no functional myotomal neuromuscular junctions before this age. We suggest that the mammalian myotome has entirely lost the function of neurally controlled muscular contraction: its remaining functions are likely to be as a signaling tissue, as a structural scaffold, and as an incubator for myogenic precursors of the deep back, abdominal, and intercostal muscles.
分节的肌肉肌节是所有脊椎动物中最早形成的肌肉。在鱼类和两栖类胚胎中，肌节很早就接受神经支配，对幼体游泳至关重要。然而，它在鸟类和哺乳动物中的作用尚不清楚。通过对大鼠胚胎切片和整体标本进行免疫组织化学研究，我们发现哺乳动物的肌节在3天的时间里进行分化和发育，在此期间并未受到生长中的脊神经的侵入。相比之下，从能够检测到肌细胞分化的那一刻起，肢体肌肉团就充满了细小的神经分支。此外，我们还发现哺乳动物的肌节直到胚胎第13.5天之后才表达成簇的乙酰胆碱受体，这一时期对应于其向成年轴上肌转变的开始，表明在此年龄之前不存在功能性的肌节神经肌肉接头。我们认为哺乳动物的肌节已经完全丧失了神经控制肌肉收缩的功能：其剩余功能可能是作为信号组织、结构支架以及深部背部、腹部和肋间肌的成肌前体细胞的孵化器。
