Cell Recognition in the developing Drosophila Brain

描述（由申请人提供）：果蝇Dscam基因编码一个庞大的免疫球蛋白（Ig）超家族蛋白家族，并在发育过程中调节精确组织的神经回路的形成中起关键作用。选择性剪接产生超过38,016种不同的同工异构体，包括19,008个外结构域，通过两个可选的跨膜片段之一连接到膜上。这些结构域具有相同的结构域结构，但在三个可变结构域Ig2、Ig3和Ig7内的氨基酸序列不同。共享相同可变结构域组合的同工异构体（即它们在每个可变结构域上都匹配）彼此结合，但它们不与其他同工异构体结合。基因分析显示，Dscam在一种被称为自我回避的现象中起着至关重要的作用。每个神经元表达一种独特的同种异构体组合，这使得它的神经突能够区分自我和非自我。自我识别，即同一细胞的神经突之间的同种异型特异性亲同性结合，促进了这些过程之间的排斥。自我回避在轴突分支的分离和树突场的形成中起着重要的作用，从而有助于神经回路的组装。在本建议中，我们将探讨三个问题：1.我们将讨论三个问题。亲同性识别对Dscam的所有功能都至关重要吗？为了解决这个问题，我们将产生Dscam的敲入突变体，它已经失去了参与亲同性结合的能力；2. 特定的Dscam亚型是否在不同的神经元群体中表达？虽然Dscam明显在自我回避中起作用，但仍有可能不同的神经元群体可能使用特定的Dscam亚型来识别其他神经元。这一目的是为了识别这些细胞；和3。它们在特定神经元中是否需要不同的替代Ig域？为了解决这个问题，我们将产生具有单个Ig2结构域、单个Ig3结构域或单个Ig7结构域的单独果蝇系。虽然在哺乳动物中没有观察到Dscam的多样性，但Dscam以一种细胞类型特异性的方式表达，似乎在小鼠无突细胞的自我回避中起类似的作用。由于人类Dscam的剂量与唐氏综合征有关，因此本文所述的研究可能为与该综合征相关的智力迟钝的病因提供见解。与公共卫生相关的神经回路由大量细胞组成，它们以一种精确的方式相互连接或“连接”在一起。这些连接模式在决定从简单的蠕虫到人类的行为方面起着至关重要的作用。这一提议的目的是了解一个与人类基因密切相关的果蝇基因是如何在发育过程中促进精确连接模式的形成的。

DESCRIPTION (provided by applicant): The Drosophila Dscam gene encodes a vast family of immunoglobulin (Ig) superfamily proteins and plays a crucial role in regulating the formation of precisely organized neural circuits during development. Alternative splicing generates more than 38,016 different isoforms, including 19,008 ectodomains tethered to the membrane by one of two alternative transmembrane segments. These ectodomains share the same domain structure, but differ in amino acid sequence within three variable domains, Ig2, Ig3 and Ig7. Isoforms sharing the same combination of variable domains (i.e. they match at each variable domain) bind to each other, but they do not bind to other isoforms. Genetic analysis has revealed that Dscam plays a crucial role in a phenomenon called self-avoidance. Each neuron expresses a unique combination of isoforms and this allows its neurites to distinguish between self and non-self. Self-recognition, namely isoform-specific homophilic binding between neurites of the same cell, promotes repulsion between these processes. Self-avoidance plays an important role in the segregation of axon branches and the elaboration of dendritic fields and, thereby, contributes to the assembly of neural circuits. In this proposal, we will address three questions: 1. Is homophilic recognition crucial for all of Dscam's functions? To address this question we will generate knock-in mutants of Dscam which have lost the ability to engage in homophilic binding; 2. Are specific isoforms of Dscam expressed in distinct populations of neurons? While Dscam clearly plays a role in self-avoidance, it remains possible that different populations of neurons may use specific isoforms of Dscam to recognize other neurons. This aim is directed towards identifying such cells; and 3. Are their requirements in specific neurons for different alternative Ig domains? To address this question we will generate separate lines of flies with a single Ig2 domain, a single Ig3 domain or a single Ig7 domain. While Dscam diversity is not observed in mammals, Dscam is expressed in a cell-type specific fashion and appears to play an analogous function in self-avoidance in mouse amacrine cells. As the dosage of human Dscam has been implicated in Down Syndrome the studies described here may provide insight into the etiology of mental retardation associated with this syndrome. PUBLIC HEALTH RELEVANCE Neural circuits comprise large ensembles of cells connected to each other or "wired up" in a precise fashion. These patterns of connections play a crucial role in determining behavior from simply worms to humans. The goal of this proposal is to understand how one fruit fly gene, closely related to a human gene, facilitates the formation of precise patterns of connections during development.