MOLECULAR ANALYSIS OF AXON FASCICLE SPECIFIC GLYCOPROTEI

理解大脑发育的一个核心问题是获得 深入了解细胞识别的分子基础以及如何 建立精确的神经元连接。在早期发育过程中 轴突必须开辟新的途径，通过未知的胚胎景观 既在中枢神经系统内也在外周神经系统内外。这些途径反过来 可以作为后来分化神经元的指导， 已经被证明可以做出高度特异性的途径选择， 选择性肌束震颤这一过程可能在以下方面发挥关键作用： 神经系统的正确布线大多数关于 选择性肌束震颤的机制涉及特异性粘附或 轴突和/或生长锥之间的识别事件 大分子然而，挑战在于检验这一假设， 鉴定和表征这些分子，因为更特异和 限制它们的表达和分布，它们的丰度就越低。 因此，已经分离出非常有限数量的分子， 提出的粘附和识别功能，其中只有少数是 仅限于轴突的子集，而不仅仅涉及一般的神经细胞 粘连 本建议的目的是增加我们对这种情况的了解， 通过确定抗原的分子结构和功能来分析分子 被单克隆抗体LAN 3-2和LAN 4-2识别， 其它抗原限定形成特异性的轴突的小子集， 在水蛭里的束。从抗原的氨基酸序列， 是一种膜表面糖蛋白，我们将分析其功能 其结构的影响。具体地说，我们想检验这个假设 这些抗原介导选择性轴突成束， 可能代表参与神经元识别和轴突引导的分子。 我们还将进行基因位点的分子表征， 探索它的精细结构，它的表达和作用方式， 发展在水蛭中克隆这些抗原的前景是， 它们对非常小且明确的轴突群体是特异性的 因此不太可能只是介导一般的粘附。 我们的长期目标是分析lan 3-2/4-2抗原和其他水蛭 轴突和轴突亚群特异性抗原是获得基本的见解 这些分子的功能意义，它们可能的 层级组织、功能决定因素和发展 表达调控。由于已经确定许多重要的 结构蛋白序列基序在功能上是保守的 在整个进化过程中，这些研究应该加强我们的基本知识， 理解神经元识别和选择性束颤， 深入了解异常神经连接的根本原因 以及大脑发育异常

A central problem in understanding the development of the brain is to gain insight into the molecular basis for cellular recognition and for how precise neuronal connections are established. During early development axons must pioneer novel pathways through uncharted embryonic landscapes both within the CNS and to and from the periphery. These pathways in turn may serve as a guide for later differentiating neurons, the axons of which have been shown to make highly specific pathway choices and to show selective fasciculation. This process may play a crucial role in the correct wiring of the nervous system. Most hypotheses about the molecular mechanism for selective fasciculation involve specific adhesion or recognition events between axons and/or growth cones mediated by surface macromolecules. However, the challenge has been to test this hypothesis and to identify and characterize such molecules, since the more specific and restricted their expression and distribution is, the lower their abundance. Consequently, a very limited number of molecules has been isolated with proposed adhesion and recognition functions and only a handful of these are confined to subsets of axons and not just involved in general neural cell adhesion. The object of the present proposal is to increase our knowledge of such molecules by determining the molecular structure and function of an antigen recognized by the monoclonal antibodies lan 3-2 and lan 4-2 as well as other antigens which define small subsets of axons forming specific fascicles in the leech. From the amino acid sequence of the antigen, which is a membrane surface glycoprotein, we will analyze the functional implications of its structure. Specifically, we want to test the hypothesis that these antigens are mediating the selective axon fasciculation and thus may represent molecules involved in neuronal recognition and axon guidance. We will also carry out a molecular characterization of the gene locus by exploring its fine structure, its expression and mode of action during development. The promise of cloning these antigens in the leech is that they are specific for a very small and well defined populations of axons and therefore are not likely to be just mediating general adhesion. Our long range goal in analyzing the lan 3-2/4-2 antigen and other leech antigens specific for axons and axonal subsets is to gain basic insights into the functional significance of such molecules, their possible hierarchial organization, functional determinants, and developmental regulation of expression. Since it has been established that many important structural protein sequence motifs have been functionally conserved throughout evolution these investigations should enhance our basic understanding of neuronal recognition and selective fasciculation and provide insights into the underlying causes of aberrant neural connections and abnormal brain development.