Yamagata M, Herman J P, Sanes J R
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
J Neurosci. 1995 Jun;15(6):4556-71. doi: 10.1523/JNEUROSCI.15-06-04556.1995.
The optic tectum is the major synaptic target of retinal axons in birds. In the chick, retinal ganglion cell axons enter the optic tectum through a superficial lamina (the stratum opticum), extended branches into deeper laminae, and arborize in specific "retinorecipient" laminae, where they form synapses. Studies using an organotypic culture system have provided evidence that the tectum bears a series of distinct, lamina-specific, cell surface-associated cues that direct these axonal behaviors (Yamagata and Sanes, 1995). Here, we have used a panel of antibodies to 30 membrane and matrix components to ask whether known adhesive molecules are distributed in lamina-specific patterns. Among many spatiotemporal pattern of expression documented, three were particularly noteworthy: (1) The cell adhesion molecules NgCAM/L1 and TAG-1/axonin-1 were concentrated in the stratum opticum. (2) SC1/JC7/DM-GRASP/BEN, N-cadherin, neuropilin, polysialylated N-CAM, and glycoconjugates recognized by the lectin VVA-B4 were concentrated in retinorecipient laminae. (3) Neurofascin, tenascin-C/cytotactin, and a matrix molecule defined by the "Sigma" antibody were present at highest levels in areas that border the retinorecipient laminae. Some members of each group (NgCAM/L1, TAG-1/axonin, SC1/JC7, polysialic acid, VVA-B4-receptors, and neurofascin) appeared on schedule and in lamina-restricted patterns in tecta from embryos that had been enucleated before retinal axons left the eye. Thus, molecules in these three categories could provide signals to retinal axons that promote extension through the stratum opticum, induce arborization or synaptogenesis in retinorecipient laminae, and prevent sprouting into adjoining laminae. Interestingly, N-cadherin accumulated in retinorecipient laminae only following the onset of synapse formation, and failed to accumulate in enucleated tecta. Immunoelectron microscopy of normal tecta demonstrated the presence of N-cadherin in the synaptic cleft, suggesting a role for this molecule in synaptic maintenance.
视顶盖是鸟类视网膜轴突的主要突触靶区。在小鸡中，视网膜神经节细胞轴突通过一个浅层板层（视层）进入视顶盖，延伸至更深层板层并分支，在特定的“视网膜接受”板层形成树突，在那里它们形成突触。使用器官型培养系统进行的研究表明，视顶盖带有一系列不同的、板层特异性的、细胞表面相关的线索，这些线索指导着这些轴突行为（山形和塞尼斯，1995年）。在这里，我们使用了一组针对30种膜和基质成分的抗体，来研究已知的黏附分子是否以板层特异性模式分布。在记录的许多时空表达模式中，有三种特别值得注意：（1）细胞黏附分子NgCAM/L1和TAG-1/轴突素-1集中在视层。（2）SC1/JC7/DM-GRASP/BEN、N-钙黏蛋白、神经纤毛蛋白、多唾液酸化N-CAM以及凝集素VVA-B4识别的糖缀合物集中在视网膜接受板层。（3）神经束蛋白、腱生蛋白-C/细胞触蛋白以及由“西格玛”抗体定义的一种基质分子在与视网膜接受板层相邻的区域含量最高。每组中的一些成员（NgCAM/L1、TAG-1/轴突素、SC1/JC7、多唾液酸、VVA-B4受体和神经束蛋白）在视网膜轴突离开眼睛之前已摘除眼球的胚胎的视顶盖中按时并以板层受限模式出现。因此，这三类分子可以向视网膜轴突提供信号，促进其通过视层延伸，诱导在视网膜接受板层的树突形成或突触形成，并防止向相邻板层的出芽。有趣的是，N-钙黏蛋白仅在突触形成开始后才在视网膜接受板层中积累，并且在摘除眼球的视顶盖中未能积累。正常视顶盖的免疫电子显微镜检查表明突触间隙中存在N-钙黏蛋白，表明该分子在突触维持中起作用。
