CARBOHYDRATES AND LECTINS IN NEURAL DEVELOPMENT

由细胞接触介导的细胞-细胞识别有助于 在神经发育过程中形成特定的突触连接。 定位于细胞表面、固有的结构多样性和调节 表达是归因于碳水化合物部分的性质， 糖缀合物也被预期具有细胞识别性， 分子。对于细胞表面的碳水化合物来介导， 然而，应该存在内源性蛋白受体（凝集素）， 识别和区分寡糖配体。一种新型 果蝇的蛋白质，称为“胶质凝集素”，就是这样一种凝集素。 通过基于粘附的表达克隆鉴定，胶质凝集素是 由胚胎中线的神经胶质细胞亚群表达， 果蝇的神经系统Gliolectin的时空表达 模式将其定位为介导神经胶质/神经或神经胶质/神经胶质相互作用 在 引导胚胎轴突连合的形成。胶质凝集素的改变 表达（部分功能丧失突变）破坏轴突生长 早期发展。为了确定胶质凝集素在轴突导向中的作用， 该提案利用了遗传和分子分析的潜力， 研究果蝇的发育所提供的功能。表型 与胶质细胞凝集素基因的无效突变相关，与异位- 胶质凝集素蛋白的表达以及与联合收割机 胶质凝集素突变与果蝇中其他活性基因的突变 将对中线进行表征。免疫电镜检查 胶质细胞凝集素的正常表达模式将表明胶质细胞凝集素是否存在于 在中线胶质细胞之间或胶质细胞和轴突之间的界面处， 这一区别对于解释突变体表型很重要。此外，胶质凝集素 碳水化合物结合将在体外和原位进一步表征， 定义结合特异性控制特异性的程度， 细胞识别这些互补的遗传、超微结构和 生物化学方法将确定胶质凝集素的功能，并将其置于 其他分子活动的背景，建议指导轴突生长 穿过果蝇的中线保守的分子表达和 发育功能表明果蝇腹侧中线 类似于脊椎动物神经管的底板。因此， 脊椎动物胶质凝集素同源物鉴定将凝集素置于 脊椎动物连合轴突寻路的关键交叉点。 阐明神经组织中的细胞识别机制，包括 碳水化合物介导的相互作用，是实现全面 CNS损伤后的功能性再生。

Cell-cell recognition mediated by cellular contact contributes to the formation of specific synaptic connectivity during neural development. Localization to the cell surface, inherent structural diversity and regulat expression are properties ascribed to the carbohydrate moieties of glycoconjugates that are also to be expected of cellular recognition molecules. For cell surface carbohydrates to mediate, cell-cell interaction however,, endogenous protein receptors (lectins) should exist that recognize and discriminate between oligosaccharide ligands. A novel Drosophila melanogaster protein, called "gliolectin", is such a lectin. Identified through adhesion-based expression cloning, gliolectin is expressed by a subset of the glial cells at the midline of the embryonic Drosophila nervous system. Gliolectin's spatial and temporal expression pattern positions it to mediate the glia/neural or glia/glial interactions at guide formation of embryonic axonal commissures. Alterations in gliolectin expression (partial loss-of-function mutations) disrupt axonal outgrowth early in development. To define gliolectin's role in axonal guidance, this proposal takes advantage of the potential for genetic and molecular analysi of function offered by studying development in Drosophila. Phenotypes associated with null mutations in the gliolectin gene, with ectopic- expression of gliolectin protein and with double mutants that combine gliolectin mutations with mutations in other genes active at the Drosophila midline will be characterized. Immuno-electron microscopic examination of gliolectin's normal expression pattern will indicate whether gliolectin lie at the interface between midline glial cells or between glia and axon, a distinction important for interpreting mutant phenotypes. Also, gliolectin' carbohydrate binding will be further characterized in vitro and in situ to define the degree to which binding specificity controls specificity in cellular recognition. These complementary genetic, ultrastructural and biochemical approaches will define gliolectin's function and place it in th context of other molecular activities suggested to guide axon outgrowth across the Drosophila midline. Conserved molecular expression and developmental function have suggested that the Drosophila ventral midline is analogous to the floorplate of the vertebrate neural tube. Therefore, th identification of a vertebrate gliolectin homologue will place a lectin at crucial crossing point for vertebrate commissural axon pathfinding. Elucidation of cellular recognition mechanisms in neural tissue, including carbohydrate-mediated interactions, is essential for realization of full functional regeneration following CNS injury.