The Role of DSCAM in Retinal Morphology and Function

描述（由申请人提供）：神经发育障碍很常见，对患者及其家人的健康构成重大负担。对正常和疾病状态下神经元发育的更好理解将有助于一般生物学知识，也可能导致对此类疾病的预防或治疗。小鼠视觉系统是研究这种现象的特别有用的模型系统，因为它已经在分子、细胞和生理水平上被广泛研究，并且通过研究视网膜神经元学到的原理可能普遍适用于大脑中的神经元。申办方实验室最近的研究揭示了唐氏综合征细胞粘附分子（Dscam）和相关Dscaml 1基因（以下统称为Dscams）在小鼠视网膜神经元自我回避中的作用。顾名思义，Dscam位于与唐氏综合症有关的人类21号染色体的关键区间内。在没有DSCAM或DSCAML 1的情况下，在正常表达该蛋白的视网膜神经元亚群中观察到细胞类型特异性聚集和树突成束。在野生型眼睛中，这些神经元均匀分布，它们的神经突很少自交。长期以来，人们一直认为视网膜神经元的间距和形态对于视觉信息的忠实处理是重要的，Dscam突变小鼠代表了第一个直接测试这一假设的适当系统。在具体目标1中，我将使用机器人图像形成和非图像形成视觉的既定行为测试来评估Dscams突变引起的解剖结构改变的功能后果。由于功能性突触仍然在突变体中形成，而非图像形成视觉任务不太可能依赖于地形图，我的假设如下：1）在特定行为所需的细胞类型因Dscams丢失而被破坏的情况下，图像形成视觉将受到负面影响，2）非图像形成视觉将保持完整。初步数据测试的视动和瞳孔反应支持这些假设。在具体目标2，我将奋进了解DSCAM功能的分子机制，并确定其他重要的神经元形态发生蛋白。这将通过利用已知的DSCAM的C-末端与MAGI（具有反向结构域结构的膜相关鸟苷酸激酶）的六个PDZ结构域之一来实现。我将免疫沉淀DSCAM/MAGI复合物，并通过质谱鉴定其他蛋白质组分。我假设，确定的蛋白质将分为两类：信号转导蛋白，介导细胞内信号的DSCAM，和蛋白质类似的DSCAM，同时结合到其他PDZ结构域的MAGI，也参与了有关细胞类型的信息通信。这种多层次的方法将是一种有效的手段，阐明神经发育障碍，如唐氏综合征的发病机制和一般的神经生物学原则的发展。

DESCRIPTION (provided by applicant): Neurodevelopmental disorders are common and represent a significant burden to the well-being of patients and their families. A greater understanding of neuronal development in both the normal and disease states will contribute to general biological knowledge and may also lead to preventions or cures for such disorders. The mouse visual system is a particularly useful model system to study such phenomena as it has been extensively studied on the molecular, cellular, and physiological levels and the principles learned by studying retinal neurons are likely to be generally applicable to neurons in the brain. Recent studies from the sponsor's laboratory have revealed a role for the Down syndrome cell adhesion molecule (Dscam) and the related Dscaml1 genes (hereafter collectively referred to as Dscams) in self-avoidance of neurons within the mouse retina. As its name suggests, Dscam is found within the critical interval of human chromosome 21 implicated in Down syndrome. In the absence of DSCAM or DSCAML1, cell type-specific aggregation and dendrite fasciculation is seen in the subsets of retinal neurons that would normally express the protein. In the wild-type eye, these neurons are evenly spaced and their neurites rarely self-cross. It has long been assumed that the spacing and morphology of retinal neurons is important for the faithful processing of visual information, and Dscam mutant mice represent the first appropriate system to directly test this hypothesis. In Specific Aim 1, I will use established behavioral tests of bot image-forming and non-image-forming vision to assess the functional consequences of the altered anatomy caused by mutations in Dscams. Since functional synapses still form in the mutant and non-image-forming visual tasks are less likely to depend on a topographical map, my hypotheses are as follows: 1) image-forming vision will be negatively affected in cases where the cell type(s) necessary for the given behavior have been disrupted by loss of Dscams, and 2) non-image-forming vision will remain intact. Preliminary data from tests of optomotor and pupillary responses support these hypotheses. In Specific Aim 2, I will endeavor to understand the molecular mechanisms of DSCAM function and to identify additional proteins important for neuronal morphogenesis. This will be accomplished by exploiting the known association of the C-terminus of DSCAMs with one of the six PDZ domains of MAGIs (membrane-associated guanylate kinases with inverted domain structure). I will immunoprecipitate DSCAM/MAGI complexes and identify additional protein components via mass spectrometry. I hypothesize that the proteins identified will fall into two categories: signal transduction proteins that mediate intracellular signaling of DSCAM, and proteins similar to DSCAM that simultaneously bind to other PDZ domains of MAGIs and which are also involved in communicating information regarding cell type. This multi-level approach will be an effective means of elucidating both the pathogenesis of neurodevelopmental disorders such as Down syndrome and general neurobiological principles of development.