Cell Recognition in the developing Drosophila Brain

描述(申请人提供)：果蝇Dscam基因编码免疫球蛋白(Ig)超家族蛋白的一个庞大家族，并在调节发育过程中精确组织的神经回路的形成方面发挥关键作用。选择性剪接产生超过38,016种不同的异构体，包括19,008个胞外结构域，通过两个替代跨膜片段中的一个连接到膜上。这些胞外区具有相同的结构域结构，但在IG2、IG3和IG7这三个可变区内的氨基酸序列不同。共享相同可变区组合的异构体(即它们在每个可变区匹配)相互结合，但它们不与其他异构体结合。基因分析显示，Dscam在一种名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异构体组合，这使得它的神经突起能够区分自我和非我。自我识别，即同一细胞的神经突起之间的同型特异性同型结合，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域的细化中起着重要作用，从而有助于神经回路的组装。在这项提案中，我们将解决三个问题：1.同性恋识别对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，这些突变体已经失去了参与同嗜性结合的能力；2.Dscam的特定亚型是否在不同的神经元群体中表达？虽然Dscam显然在自我回避中发挥了作用，但不同的神经元群体仍有可能使用特定的Dscam亚型来识别其他神经元。这一目的是为了识别这类细胞；以及3.它们在特定神经元中是否对不同的替代Ig结构域有需求？为了解决这个问题，我们将生成具有单个IG2域、单个IG3域或单个IG7域的单独的果蝇行。虽然在哺乳动物中没有观察到Dscam的多样性，但Dscam以一种细胞类型特有的方式表达，并似乎在小鼠无长突细胞中发挥着类似的自我回避功能。由于人类Dscam的剂量与唐氏综合症有关，这里描述的研究可能为了解与唐氏综合症相关的精神发育迟缓的病因提供洞察力。与公共健康相关的神经回路由相互连接或以精确方式“连线”的大型细胞集合组成。这些连接模式在决定从简单的蠕虫到人类的行为方面发挥着至关重要的作用。这项提议的目标是了解一个与人类基因密切相关的果蝇基因如何促进发育过程中精确的连接模式的形成。

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.