DETERMINANTS OF GLOMERULAR ORGANIZATION

多种证据支持这样的观点，即表达相同气味受体(OR)的嗅觉感受器神经元的轴突在很大程度上汇聚到嗅球中的两个或几个肾小球上。要做到这一点，在嗅觉上皮和嗅球之间有一种非同寻常的轴突重组。轴突在重组过程中表现出的路径发现以及它们对特定肾小球的靶向似乎至少部分地受到任何单个嗅觉感受器神经元表达的独特OR的影响。因此，ORS构成了一组独特的分子标签/决定因素，为进一步研究肾小球的组织及其在气味处理中的作用提供了令人兴奋的机会。。此外，由于蛋白质追踪技术的最新进展，有机会研究嗅觉感受器神经元中ORS的时空蛋白质，以了解它们在细胞内的分布是否与轴突引导中的决定作用一致。提出了三个具体的目标：1)编码OR序列的一个特定基因是否唯一地定义了所有投射到一个小球的传入轴突？利用Lac-Z结构，将研究表达特定ORS的轴突的突触组织。2)顶端树突支配特定肾小球的二尖瓣细胞的分布是什么？虽然一些证据表明这些二尖瓣细胞的胞体应该是相连的，但这一假设尚未得到解决。绿色荧光蛋白构建物可用于识别汇聚在特定肾小球上的传入轴突。被识别的肾小球将被荧光或光密度示踪剂感染，以绘制其树突支配被识别的肾小球的二尖瓣细胞的分布。3)OR蛋白在细胞内的分布是什么？虽然支持ORS具有多种作用的证据是令人信服的，但在哪些细胞内隔间或蛋白质中发现并不明显。利用绿色荧光蛋白编码序列与OR编码序列的融合，将评估OR蛋白产物的时空特征，以解决我们知识中的这一重大差距。总而言之，这些研究将为初级嗅觉投射的组织、肾小球在气味处理中的作用、从肾小球发出的更高级别投射的地形图以及可能控制OR蛋白在细胞内分布的机制提供新的线索。这些结果可能对患有嗅觉障碍和嗅觉减退、卡尔曼综合征以及轴突引导相关疾病的人具有重要意义。

Multiple lines of evidence support the notion that the axons from olfactory receptor neurons expressing the same odor receptor (OR) largely converge onto only 2 or a few glomeruli in the olfactory bulb. To accomplish this there is an extraordinary reorganization of axons that occurs between the olfactory epithelium and the olfactory bulb. The pathfinding exhibited by axons during reorganization as well as their targeting of specific glomeruli appears to be influenced, at least in part, by the unique OR expressed by any single olfactory receptor neuron. Thus, ORS constitute a unique set of molecular tags/determinants that provide an exciting opportunity to study further the organization of the glomerulus and its role in odor processing. . Moreover, because of recent advances in protein tracking technology, the opportunity is presented to investigate the spatio-temporal proteins of ORS in olfactory receptor neurons in order to understand if their intracellular distribution is consistent with a determinant role in axon guidance. Three specific aims are proposed: 1) Does one specific gene, coding an OR sequence, uniquely define all of the afferent axons projecting to one glomerulus? Using Lac-Z constructs, the synaptic organization of axons expressing specific ORS will be studied. 2) What is the distribution of mitral cells whose apical dendrites innervate a specific glomerulus? While some evidence suggests that the somata of these mitral cells should be contiguous, the hypothesis has not been addressed. Green Fluorescent Protein constructs can be employed to identify the afferent axons converging on specific glomeruli. Identified glomeruli will be infected with fluorescent or light-dense tracers to map the distribution of mitral cells whose dendrites are innervating the identified glomerulus. 3) What is the intracellular distribution of OR protein? While the evidence favoring multiple roles for ORS is compelling, it is not evident in which intracellular compartments OR protein is found. Using Green Fluorescent Protein coding sequence fusions with OR coding sequences, the spatio- temporal characteristics of OR protein products will be assessed to address this significant gap in our knowledge. Collectively, these studies will shed new light on the organization of primary olfactory projections, the role of the glomerulus in odor processing, the topography of higher order projections emerging from glomeruli and finally, the mechanisms that may govern the intracellular distribution of OR proteins. These results may be significant for people suffering from anosmia and hyposmia, Kalman's Syndrome and related diseases of axon guidance.