DETERMINANTS OF GLOMERULAR ORGANIZATION

多种证据支持这一观点，即来自嗅觉受体神经元的轴突表达相同的气味受体（OR），大部分集中在嗅球的2个或几个肾小球上。为了达到这个目的，在嗅上皮和嗅球之间的轴突发生了非同寻常的重组。轴突在重组过程中表现出的寻路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受体神经元表达的独特OR的影响。因此，ORS构成了一组独特的分子标记/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，由于蛋白质跟踪技术的最新进展，我们有机会研究嗅觉受体神经元中ORS的时空蛋白，以了解它们在细胞内的分布是否与轴突引导的决定性作用相一致。提出了三个具体目标：1)编码OR序列的特定基因是否唯一地定义了投射到一个肾小球的所有传入轴突？使用Lac-Z结构，将研究表达特异性ORS的轴突的突触组织。2)尖顶树突支配特定肾小球的二尖瓣细胞分布如何？虽然一些证据表明这些二尖瓣细胞的躯体应该是相邻的，但这一假设尚未得到解决。绿色荧光蛋白结构可用于识别汇聚到特定肾小球的传入轴突。确定的肾小球将被荧光或光密集示踪剂感染，以绘制树突支配确定肾小球的二尖瓣细胞的分布。3) OR蛋白在细胞内的分布如何？虽然支持ORS多重作用的证据是令人信服的，但尚不清楚在哪些细胞内区室中发现了OR蛋白。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空白。总的来说，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、肾小球产生的高阶投射的地形以及最终可能控制OR蛋白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缺失和嗅觉减退症、卡尔曼综合征和轴突引导相关疾病的人有重要意义。

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.