Becker C G, Meyer R L, Becker T
Zentrum für Molekulare Neurobiologie Hamburg, Universität Hamburg, D-20246 Hamburg, Germany.
J Comp Neurol. 2000 Nov 20;427(3):469-83.
Regeneration of optic axons in the continuously growing optic system of adult zebrafish was analyzed by anterograde tracing and correlated with the mRNA expression patterns of the recognition molecules ephrin-A2 and ephrin-A5b in retinal targets. The optic tectum and diencephalic targets are all reinnervated after a lesion. However, the rate of erroneous pathway choices was increased at the chiasm and the bifurcation between the ventral and dorsal brachium of the optic tract compared to unlesioned animals. Tracer application to different retinal positions revealed retinotopic reinnervation of the tectum within 4 weeks after the lesion. In situ hybridization analysis indicated the presence of rostral-low to caudal-high gradients of ephrin-A2 and ephrin-A5b mRNAs in unlesioned control tecta and after a unilateral optic nerve lesion. By contrast, the parvocellular superficial pretectal nucleus showed retinotopic organization of optic fibers but no detectable expression of ephrin-A2 and ephrin-A5b mRNAs. However, a row of cells delineating the terminal field of optic fibers in the dorsal part of the periventricular pretectal nucleus was intensely labeled for ephrin-A5b mRNA and may thus provide a stop signal for ingrowing axons. Ephrin-A2 and ephrin-A5b mRNAs were not detectable in the adult retina, despite their prominent expression during development. Thus, given a complementary receptor system in retinal ganglion cells, expression of ephrin-A2 and ephrin-A5b in primary targets of optic fibers in adult zebrafish may contribute to guidance of optic axons that are continuously added to the adult projection and of regenerating axons after optic nerve lesion.
通过顺行示踪分析成年斑马鱼持续生长的视觉系统中视神经轴突的再生情况，并将其与视网膜靶标中识别分子ephrin-A2和ephrin-A5b的mRNA表达模式相关联。视顶盖和间脑靶标在损伤后均会重新获得神经支配。然而，与未损伤的动物相比，在视交叉以及视束腹侧和背侧臂之间的分叉处，错误路径选择的发生率有所增加。将示踪剂应用于不同的视网膜位置显示，损伤后4周内视顶盖实现了视网膜拓扑重支配。原位杂交分析表明，在未损伤的对照视顶盖以及单侧视神经损伤后，ephrin-A2和ephrin-A5b mRNA存在从吻侧低到尾侧高的梯度。相比之下，小细胞浅层顶盖前核显示出视神经纤维的视网膜拓扑组织，但未检测到ephrin-A2和ephrin-A5b mRNA的表达。然而，在脑室周围顶盖前核背侧界定视神经纤维终末场的一排细胞中，ephrin-A5b mRNA被强烈标记，因此可能为生长中的轴突提供一个停止信号。尽管ephrin-A2和ephrin-A5b在发育过程中表达显著，但在成年视网膜中未检测到它们的mRNA。因此，鉴于视网膜神经节细胞中存在互补的受体系统，成年斑马鱼视神经纤维主要靶标中ephrin-A2和ephrin-A5b的表达可能有助于引导不断添加到成年投射中的视神经轴突以及视神经损伤后再生的轴突。
