Target Specificity in the Drosophila Olfactory System

描述（由申请人提供）：果蝇的嗅觉系统为探索神经元在发育过程中形成连接的机制提供了独特的机会。表达相同气味受体的嗅觉受体神经元（ORN）连接到触角叶中的相同神经元，而表达不同气味受体的神经元连接到不同的神经元。这里提出的研究旨在了解这种特异性的分子基础。遗传研究表明，不同的神经元使用不同的细胞表面蛋白质星座来控制特异性，包括Dscam，N-钙粘蛋白，Lar受体酪氨酸磷酸酶和新的钙粘蛋白，火烈鸟。特别令人感兴趣的是对Dscam的要求。Dscam是可变剪接的，有许多不同的形式（大约38，000种），可能有助于识别特异性。在这个提议中，将测试不同形式的Dscam在控制嗅觉系统中神经元连接的特异性方面的作用。提出了三组实验来严格评估替代形式的Dscam在ORN靶向中的重要性。首先，一组删除已被隔离，删除许多不同形式的Dscam。将在这些突变体中评估这些突变对一组三种不同ORN的影响。将分离缺乏其他形式的其他突变体，并探索它们对ORN靶向的影响。其次，同源重组将用于将含有Dscam形式的单个胞外结构域引入内源Dscam基因座中。这将使多样性从大约38，000减少到2种形式。将评估三组嗅觉神经元的表型。最后，单一形式的Dscam将在野生型和突变体背景中在异源启动子下表达。将评估这些形式诱导的显性表型。将评估不诱导显性表型的形式挽救功能完全丧失的Dscam突变的能力。更好地了解神经元连接在发育过程中是如何形成的，将有助于深入了解可能在各种神经和精神疾病中被破坏的机制。

DESCRIPTION (provided by applicant): The olfactory system in Drosophila melanogaster provides a unique opportunity to explore the mechanisms by which neurons form connections during development. Olfactory receptor neurons (ORNs) that express the same odorant receptors connect to the same neurons in the antennal lobe, while neurons that express different odorant receptors connect to different neurons. The studies proposed here are directed towards understanding the molecular basis of this specificity. Genetic studies have revealed that different neurons use different constellations of cell surface proteins to control specificity including Dscam, N-cadherin, Lar receptor tyrosine phosphatase and the novel cadherin, Flamingo. Of particular interest is the requirement for Dscam. Dscam is alternatively spliced and comes in many different forms (approximately 38,000) that may contribute to recognition specificity. In this proposal, the role of different forms of Dscam in controlling the specificity of neuronal connections in the olfactory system will be tested. Three sets of experiments are proposed to critically assess the importance of alternative forms of Dscam in ORN targeting. First, a set of deletions has been isolated that remove many different forms of Dscam. The effect of these mutations on a set of three different ORNs will be assessed in these mutants. Additional mutants lacking other forms will be isolated and their affects on ORN targeting will be explored. Second, homologous recombination will be used to introduce a single extracellular domain containing form of Dscam into the endogenous Dscam locus. This will reduce diversity from approximately 38,000 to 2 forms. The phenotypes in three sets of olfactory neurons will be assessed. And finally, single forms of Dscam will be expressed under heterologous promoters in both wild type and mutant backgrounds. Dominant phenotypes induced by these forms will be assessed. Forms that do not induce dominant phenotypes will be assessed for the ability to rescue the complete loss of function Dscam mutations. A better understanding of how neuronal connections are formed during development will provide insight into the mechanisms that may be disrupted in various neurological and psychiatric diseases.