Ward Lizzy, Pang Angel S W, Evans Susan E, Stern Claudio D
Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, U.K.
Department of Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, U.K..
Dev Biol. 2018 Jul 1;439(1):3-18. doi: 10.1016/j.ydbio.2018.04.005. Epub 2018 Apr 11.
The vertebral column is segmented, comprising an alternating series of vertebrae and intervertebral discs along the head-tail axis. The vertebrae and outer portion (annulus fibrosus) of the disc are derived from the sclerotome part of the somites, whereas the inner nucleus pulposus of the disc is derived from the notochord. Here we investigate the role of the notochord in vertebral patterning through a series of microsurgical experiments in chick embryos. Ablation of the notochord causes loss of segmentation of vertebral bodies and discs. However, the notochord cannot segment in the absence of the surrounding sclerotome. To test whether the notochord dictates sclerotome segmentation, we grafted an ectopic notochord. We find that the intrinsic segmentation of the sclerotome is dominant over any segmental information the notochord may possess, and no evidence that the chick notochord is intrinsically segmented. We propose that the segmental pattern of vertebral bodies and discs in chick is dictated by the sclerotome, which first signals to the notochord to ensure that the nucleus pulposus develops in register with the somite-derived annulus fibrosus. Later, the notochord is required for maintenance of sclerotome segmentation as the mature vertebral bodies and intervertebral discs form. These results highlight differences in vertebral development between amniotes and teleosts including zebrafish, where the notochord dictates the segmental pattern. The relative importance of the sclerotome and notochord in vertebral patterning has changed significantly during evolution.
脊柱是分节的，沿着头尾轴由一系列交替的椎骨和椎间盘组成。椎骨和椎间盘的外部（纤维环）源自体节的生骨节部分，而椎间盘的内部髓核则源自脊索。在这里，我们通过在鸡胚胎中进行的一系列显微手术实验来研究脊索在椎骨模式形成中的作用。脊索消融会导致椎体和椎间盘的分节丧失。然而，在没有周围生骨节的情况下，脊索无法分节。为了测试脊索是否决定生骨节的分节，我们移植了一个异位脊索。我们发现生骨节的内在分节比脊索可能拥有的任何分节信息都更具主导性，并且没有证据表明鸡的脊索是内在分节的。我们提出，鸡的椎体和椎间盘的分节模式是由生骨节决定的，生骨节首先向脊索发出信号，以确保髓核与体节衍生的纤维环同步发育。后来，在成熟的椎体和椎间盘形成时，脊索对于维持生骨节的分节是必需的。这些结果突出了羊膜动物和硬骨鱼（包括斑马鱼）在椎骨发育上的差异，在硬骨鱼中，脊索决定分节模式。在进化过程中，生骨节和脊索在椎骨模式形成中的相对重要性发生了显著变化。
