Kryvi Harald, Rusten Iselin, Fjelldal Per Gunnar, Nordvik Kari, Totland Geir K, Karlsen Tine, Wiig Helge, Long John H
Department of Biology, University of Bergen, Bergen, Norway.
Institute of Marine Research, Bergen, Norway.
J Anat. 2017 Nov;231(5):639-654. doi: 10.1111/joa.12679. Epub 2017 Aug 8.
We present the development of the notochord of the Atlantic salmon (Salmo salar L.), from early embryo to sexually mature fish. Over the salmon's lifespan, profound morphological changes occur. Cells and gross structures of the notochord reorganize twice. In the embryo, the volume of the notochord is dominated by large, vacuolated chordocytes; each cell can be modeled as a hydrostat organized into a larger cellular-hydrostat network, structurally bound together with desmosomes. After the embryo hatches and grows into a fry, vacuolated chordocytes disappear, replaced by extracellular lacunae. The formation of mineralized, segmental chordacentra stiffens the notochord and creates intervertebral joints, where tissue strain during lateral bending is now focused. As development proceeds towards the parr stage, a process of devacuolization and intracellular filament accumulation occur, forming highly dense, non-vacuolated chordocytes. As extracellular lacunae enlarge, they are enclosed by dense filamentous chordocytes that form transverse intervertebral septa, which are connected to the intervertebral ligaments, and a longitudinal notochordal strand. In the vertebral column of pelagic adults, large vacuolated chordocytes reappear; cells of this secondary population have a volume up to 19 000 times larger than the primary vacuolated chordocytes of the early notochord. In adults the lacunae have diminished in relative size. Hydrostatic pressure within the notochord increases significantly during growth, from 525 Pa in the alevins to 11 500 Pa in adults, at a rate of increase with total body length greater than that expected by static stress similarity. Pressure and morphometric measurements were combined to estimate the stress in the extracellular material of the notochordal sheath and intervertebral ligaments and the flexural stiffness of the axial skeleton. The functional significance of the morphological changes in the axial skeleton is discussed in relation to the different developmental stages and locomotor behavior changes over the lifespan of the fish.
我们展示了大西洋鲑（Salmo salar L.）从早期胚胎到性成熟鱼类脊索的发育过程。在鲑鱼的生命周期中，会发生深刻的形态变化。脊索的细胞和大体结构会重新组织两次。在胚胎中，脊索的体积主要由大的、空泡化的脊索细胞主导；每个细胞都可以被建模为一个液压静力结构，组织成一个更大的细胞 - 液压静力网络，并通过桥粒在结构上结合在一起。胚胎孵化并成长为鱼苗后，空泡化的脊索细胞消失，被细胞外腔隙取代。矿化的、节段性的脊索中心的形成使脊索变硬，并形成椎间关节，现在侧向弯曲时的组织应变集中于此。随着发育进入幼鲑阶段，会发生空泡化消失和细胞内细丝积累的过程，形成高度密集、无空泡的脊索细胞。随着细胞外腔隙扩大，它们被密集的丝状脊索细胞包围，形成横向椎间隔膜，这些隔膜与椎间韧带相连，并形成一条纵向脊索束。在远洋成年鱼的脊柱中，大的空泡化脊索细胞再次出现；这个次级群体的细胞体积比早期脊索的初级空泡化脊索细胞大19000倍。在成年鱼中，腔隙的相对大小减小。在生长过程中，脊索内的静水压力显著增加，从仔鱼期的525帕增加到成年鱼的11500帕，其随鱼体全长的增加速率大于静态应力相似性预期的速率。结合压力和形态测量来估计脊索鞘和椎间韧带细胞外物质中的应力以及轴向骨骼的弯曲刚度。本文讨论了轴向骨骼形态变化的功能意义与鱼类生命周期中不同发育阶段和运动行为变化的关系。
