Grotmol Sindre, Kryvi Harald, Nordvik Kari, Totland Geir K
Department of Zoology, University of Bergen, Allégt 41, 5007 Bergen, Norway.
Anat Embryol (Berl). 2003 Dec;207(4-5):263-72. doi: 10.1007/s00429-003-0349-y. Epub 2003 Oct 22.
This study indicates that the development of the vertebrae in the Atlantic salmon requires the orchestration of two sources of metameric patterning, derived from the notochord and the somite rows, respectively. Before segmentation of the salmon notochord, chordoblasts exhibit a well-defined cell axis that is uniformly aligned with the cranio-caudal axis. The morphology of these cells is characterised by a foot-like basal projection that rests on the notochordal sheath. Notochordal segments are initially formed within the chordoblast layer by metameric change in the axial orientation of groups of chordoblasts. This process results in the formation of circular bands of chordoblasts, with feet perpendicular to the cranio-caudal axis, the original chordoblast orientation. Each vertebra is defined by two such chordoblast bands, at the cranial and caudal borders, respectively. Formation of the chordoblast segments closely precedes formation of the chordacentra, which form as calcified rings within the adjacent notochordal sheath. Sclerotomal osteoblasts then differentiate on the surface of the chordacentra, using them as foundations for further vertebral growth. Thus, the morphogenesis of the rudiments of the vertebral bodies is initiated by a generation of segments within the chordoblast layer. This dual segmentation model for salmon, in which the segmental patterns of the neural and haemal arches are somite-derived, while the vertebral segments seem to be notochord-derived, contrasts with current models for avians and mammals.
本研究表明，大西洋鲑鱼椎骨的发育需要协调两种节段模式来源，分别源自脊索和体节排。在鲑鱼脊索分割之前，成脊索细胞表现出明确的细胞轴，该轴与头尾轴均匀对齐。这些细胞的形态特征是有一个脚状的基底突起，位于脊索鞘上。脊索节段最初在成脊索细胞层内通过成脊索细胞群轴向方向的节段性变化形成。这个过程导致形成成脊索细胞的环形带，其脚垂直于头尾轴，即成脊索细胞的原始方向。每个椎骨分别由位于头端和尾端边界的两个这样的成脊索细胞带定义。成脊索细胞节段的形成紧接在脊索中心形成之前，脊索中心在相邻的脊索鞘内形成钙化环。然后，硬骨膜成骨细胞在脊索中心表面分化，将其作为椎骨进一步生长的基础。因此，椎体原基的形态发生是由成脊索细胞层内的节段生成启动的。鲑鱼的这种双重节段模型，其中神经弓和血弓的节段模式源自体节，而椎骨节段似乎源自脊索，这与当前鸟类和哺乳动物的模型形成对比。
