Fleming Angeleen, Keynes Roger, Tannahill David
Department of Anatomy, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK.
Development. 2004 Feb;131(4):873-80. doi: 10.1242/dev.00952. Epub 2004 Jan 21.
The vertebrates are defined by their segmented vertebral column, and vertebral periodicity is thought to originate from embryonic segments, the somites. According to the widely accepted 'resegmentation' model, a single vertebra forms from the recombination of the anterior and posterior halves of two adjacent sclerotomes on both sides of the embryo. Although there is supporting evidence for this model in amniotes, it remains uncertain whether it applies to all vertebrates. To explore this, we have investigated vertebral patterning in the zebrafish. Surprisingly, we find that vertebral bodies (centra) arise by secretion of bone matrix from the notochord rather than somites; centra do not form via a cartilage intermediate stage, nor do they contain osteoblasts. Moreover, isolated, cultured notochords secrete bone matrix in vitro, and ablation of notochord cells at segmentally reiterated positions in vivo prevents the formation of centra. Analysis of fss mutant embryos, in which sclerotome segmentation is disrupted, shows that whereas neural arch segmentation is also disrupted, centrum development proceeds normally. These findings suggest that the notochord plays a key, perhaps ancient, role in the segmental patterning of vertebrae.
脊椎动物是由其分节的脊柱所定义的，并且脊椎周期性被认为起源于胚胎节段，即体节。根据广泛接受的“重新分割”模型，单个脊椎是由胚胎两侧两个相邻体节的前半部分和后半部分重新组合形成的。尽管在羊膜动物中有支持该模型的证据，但它是否适用于所有脊椎动物仍不确定。为了探究这一点，我们研究了斑马鱼的脊椎模式形成。令人惊讶的是，我们发现椎体（椎体中心）是由脊索分泌骨基质形成的，而不是体节；椎体不是通过软骨中间阶段形成的，也不包含成骨细胞。此外，分离培养的脊索在体外分泌骨基质，并且在体内按节段重复位置消融脊索细胞会阻止椎体中心的形成。对fss突变体胚胎的分析表明，在该突变体中体节分割被破坏，虽然神经弓分割也被破坏，但椎体发育正常进行。这些发现表明，脊索在脊椎的节段模式形成中起着关键作用，也许是古老的作用。
