Currie P D, Ingham P W
Molecular Embryology Laboratory, Imperial Cancer Research Fund, London, UK.
Nature. 1996 Aug 1;382(6590):452-5. doi: 10.1038/382452a0.
The notochord plays a central role in vertebrate development, acting as a signalling source that patterns the neural tube and somites. In in vitro assays, the secreted protein Sonic hedgehog mimics the inducing effects of notochord on both presomitic mesoderm and neural plate explants of amniote embryos, suggesting that both patterning activities of the notochord may be mediated by this protein in vivo. In zebrafish, however, mutants with disrupted notochord development lack a specific muscle cell type, the muscle pioneers, although they retain the ability to induce neural differentiation, raising the possibility that neural tube and somite patterning may be mediated by distinct signals. Here we describe a new member of the hedgehog family, echidna hedgehog, that is expressed exclusively in the notochord and has the ability to rescue the differentiation of muscle pioneer cells in mutants with no notochord. Moreover, we show that a combination of ectopic echidna hedgehog and sonic hedgehog expression induces supernumary muscle pioneers in wild-type embryos, suggesting that both signals act sequentially to pattern the developing somites.
脊索在脊椎动物发育过程中起着核心作用，作为一种信号源，它为神经管和体节定型。在体外实验中，分泌蛋白音猬因子模拟了脊索对羊膜动物胚胎的前体中胚层和神经板外植体的诱导作用，这表明脊索的两种定型活动在体内可能都由该蛋白介导。然而，在斑马鱼中，脊索发育受阻的突变体缺乏一种特定的肌肉细胞类型，即肌肉先驱细胞，尽管它们仍保留诱导神经分化的能力，这增加了神经管和体节定型可能由不同信号介导的可能性。在这里，我们描述了刺猬因子家族的一个新成员，针鼹猬因子，它仅在脊索中表达，并且能够挽救无脊索突变体中肌肉先驱细胞的分化。此外，我们表明，异位表达针鼹猬因子和音猬因子的组合在野生型胚胎中诱导出额外的肌肉先驱细胞，这表明这两种信号依次作用于发育中的体节以使其定型。
