Limb muscles are formed from migratory muscle precursor cells (MMPs) that delaminate from the ventral region of dermomyotomes and migrate into the limb bud. MMPs remain undifferentiated during migration, commencing differentiation into skeletal muscle after arrival in the limb. However, it is still unclear whether the developmental mechanisms of MMPs are conserved in teleost fishes. Here, we investigate the development of pectoral fin muscles in the teleost medaka Oryzias latipes. Expression of the MMP marker lbx1 is first observed in several somites prior to the appearance of fin buds. lbx1-positive cells subsequently move anteriorly and localize in the prospective fin bud region to differentiate into skeletal muscle cells. To address the developmental mechanisms underlying fin muscle formation, we knocked down tbx5, a gene that is required for fin bud formation. tbx5 morphants showed loss of fin buds, whereas lbx1 expression initiated normally in anterior somites. Unlike in normal embryos, expression of lbx1 was not maintained in migrating fin MMPs or within the fin buds. We suggest that fin MMPs appear to undergo two phases in their development, with an initial specification of MMPs occurring independent of fin buds and a second fin bud-dependent phase of MMP migration and proliferation. Our results showed that medaka fin muscle is composed of MMPs. It is suggested that the developmental mechanism of fin muscle formation is conserved in teleost fishes including medaka. Through this study, we also propose new insights into the developmental mechanisms of MMPs in fin bud formation.

中文翻译：

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高胸鳍形成中迁移性肌肉前体的发育机制。

肢体肌肉由迁徙的肌肉前体细胞（MMP）形成，这些细胞从皮肤肌瘤的腹侧区域分层并迁移到肢体芽中。MMP在迁移过程中保持未分化状态，到达肢体后开始分化为骨骼肌。但是，目前尚不清楚硬骨鱼类中MMPs的发育机制是否得到保留。在这里，我们调查了硬骨Myyy oryzias latipes的胸鳍肌肉的发育。MMP标记lbx1的表达首先在鳍状芽出现之前的数个子节中观察到。磅x1-阳性细胞随后向前移动并定位在预期的鳍芽区域中，以分化为骨骼肌细胞。为了解决鳍状肌肉形成的发育机制，我们敲低了鳍状芽形成所需的基因tbx5。tbx5 morphant显示失去鳍芽，而lbx1表达通常在前额节开始。与正常胚胎不同，lbx1的表达未在迁移的鳍MMP或鳍芽内维持。我们建议鳍MMPs似乎经历两个阶段的发展，MMPs的初始规格独立于鳍芽而发生，而第二个依赖于鳍芽的MMP迁移和增殖阶段。我们的结果表明，aka高翅肌肉由MMP组成。有人建议在包括鱼在内的硬骨鱼中保留鳍肌肉形成的发育机制。通过这项研究，我们还提出了鳍翅形成过程中MMPs发育机制的新见解。