Bernhardt R R, Goerlinger S, Roos M, Schachner M
Department of Neurobiology, Swiss Federal Institute of Technology, Hönggerberg, Zürich.
Dev Dyn. 1998 Nov;213(3):334-47. doi: 10.1002/(SICI)1097-0177(199811)213:3<334::AID-AJA9>3.0.CO;2-4.
The ventral branches of the segmental peripheral nerves in the zebrafish embryo are pioneered by the caudal primary (CaP) motor axons, which extend midsegmentally at the interface of the somite and the notochord. The signals that define the CaP pathway are not well understood. To gain insight into the nature of the guidance cues, we have examined the environment of the CaP motor axons by using electron microscopy and histochemistry. Specifically, we have mapped the distribution of the transcription factor engrailed, of a chondrotin sulfate epitope, and of the recognition molecules zebrafish semaphorin z1b and zebrafish tenascin C. Ultrastructural examination of dye-labeled CaP motor axons revealed a close association with the medial surface of the somite but not with the notochord. The CaP axons were always accompanied by cells that appeared to migrate at the interface of somite and notochord. These cells were confined to the posterior half of the somite. Some of the cells may be neural crest derived, many others are probably of sclerotomal origin. The putative migratory cells expressed a chondroitin sulfate epitope that is a marker of sclerotome in the chick. The pathway of the CaP axon and the distribution of the putative neural crest and sclerotome cells correlated with a subdivision of the myotome into an anterior and posterior components, which were evident at the histological level and by the expression of the markers engrailed, semaphorin z1b, chondroitin sulfate, and tenascin C. We suggest that both the pathway choice of the CaP axon and the route of migratory cells reflect this anterior-posterior bipartition of the myotome.
斑马鱼胚胎节段性周围神经的腹侧分支由尾侧初级（CaP）运动轴突引导，这些轴突在体节和脊索的界面处向节段中部延伸。定义CaP通路的信号尚不清楚。为了深入了解引导线索的性质，我们使用电子显微镜和组织化学检查了CaP运动轴突的环境。具体而言，我们绘制了转录因子engrailed、硫酸软骨素表位以及识别分子斑马鱼信号素z1b和斑马鱼腱生蛋白C的分布图。对染料标记的CaP运动轴突的超微结构检查显示，它们与体节的内侧表面紧密相关，而与脊索无关。CaP轴突总是伴随着一些似乎在体节和脊索界面处迁移的细胞。这些细胞局限于体节的后半部分。其中一些细胞可能源自神经嵴，许多其他细胞可能起源于硬骨节。这些假定的迁移细胞表达了一种硫酸软骨素表位，这是鸡硬骨节的一个标记。CaP轴突的通路以及假定的神经嵴和硬骨节细胞的分布与肌节分为前后两部分相关，这在组织学水平以及通过engrailed、信号素z1b、硫酸软骨素和腱生蛋白C等标记物的表达中很明显。我们认为，CaP轴突的通路选择和迁移细胞的路径都反映了肌节的前后二分法。
