Molecular Approaches on Neuronal Cell Recognition

为了阐明特异性神经细胞识别的分子机制，我们制备了识别非洲爪哇蝌蚪神经组织中神经细胞表面蛋白的单抗，并获得了命名为B2(mab-B2)的单抗。单抗-B2识别的抗原是一种分子质量为220kd的细胞表面蛋白。我们将该细胞表面蛋白命名为丛状蛋白(从B2更名)。在这项研究中，为了了解神经丛蛋白在神经系统发育中的生物学意义，做了以下两个方面的研究。网状蛋白在视网膜组织发生中的作用：单抗-B2免疫组织化学染色显示，在神经视网膜中，网状蛋白在内层和外层均有表达。当胚胎眼在抗网织蛋白抗血清(Fab片段)的存在下培养时，视网膜网状层的形成受到阻碍。这些数据表明，网状蛋白在视网膜网状层的发育中起作用。基因克隆：克隆结果表明，该网络蛋白是一种新型的L跨膜蛋白，其胞外部分含有三个内部重复的富含半胱氨酸的簇。为了验证丛蛋白是否是一种细胞黏附分子，我们用非洲爪哇丛状蛋白cDNA导入小鼠成纤维细胞系(L细胞)。外源丛状蛋白诱导的L细胞在钙离子存在下表现出细胞黏附。本研究结果提示，细胞表面蛋白丛状蛋白参与神经细胞的识别，在神经系统发育过程中可能起重要作用。

To clarify molecular mechanisms underlaying specific neurolal cell recognition, we have produced monoclonal antibodies which recognize neuroral cell surface proteins in Xenopus tadpole nervous tissues, and obtained a monoclonal antibody named B2 (MAb-B2). The antigen recognized by MAb-B2 is a cell surface protein with 220kd in molecular weigth. We named the cell surface protein as plexin (renamed from B2). In this study, to access the biological meanings of the plexin in the developmetn of nervous sytem, the following two appraches have been done.1. Involvement of the Plexin in Retinal Histogenseis : Immunohistochemistry using MAb-B2 indicated that, in the neural retina, the plexin was expressed in both the inner and outer plexiform layrs. When embryonic eyes were cultured in the presence of anti-plexin antiserum (Fab fragments), the formation of the retinal plexiform layrs was impeded. These data suggest that the plexin plays a role in the development of retinal plexiform layrs.2. cDNA cloning : cDNA cloning reveals that the plexin is a novel type-l transmembrane protein with threeinternal repeats of cystein-rich clusters in its extracellular portion. To test whether the plexin is a cell adhesion molecule, we tranfected mouse fibraoblastic cell line (L cells) with Xenopus plexin cDNA.L cells introduced exogenous plexin showed cell adhesiveness, in the presence of Ca^<2+>. These results indicate that the plexin can mediate cell adhesion in a homophilic, Ca^<2+>-dependent manner.The results obtained in this study suggest that the cell surface protein plexin in involved in neuronal cell recognition, and may an important role in the development of nervous system.