The Role of DSCAM in Retinal Morphology and Function

描述（由申请人提供）：神经发育障碍是常见的，对患者及其家庭的福祉构成了重大负担。更好地了解正常和疾病状态下的神经元发育将有助于提高一般生物学知识，也可能导致预防或治疗这类疾病。小鼠视觉系统是研究此类现象的一个特别有用的模型系统，因为它已经在分子、细胞和生理水平上得到了广泛的研究，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。最近赞助商实验室的研究揭示了唐氏综合症细胞粘附分子（Dscam）和相关的Dscaml1基因（以下统称为dscam1）在小鼠视网膜内神经元的自我回避中的作用。顾名思义，Dscam是在与唐氏综合症有关的人类21号染色体的关键区间内发现的。在缺乏DSCAM或DSCAML1的情况下，在正常表达该蛋白的视网膜神经元亚群中可以看到细胞类型特异性聚集和树突束化。在野生型眼睛中，这些神经元是均匀间隔的，它们的神经突很少自我交叉。长期以来，人们一直认为视网膜神经元的间距和形态对视觉信息的忠实处理很重要，而Dscam突变小鼠代表了第一个直接测试这一假设的合适系统。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由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，非图像形成的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失去Dscams而中断的情况下，图像形成的视觉将受到负面影响，2)非图像形成的视觉将保持完整。验光和瞳孔反应测试的初步数据支持这些假设。在Specific Aim 2中，我将努力了解DSCAM功能的分子机制，并确定对神经元形态发生重要的其他蛋白质。这将通过利用DSCAMs的c端与MAGIs（具有倒置结构域的膜相关鸟苷酸激酶）的六个PDZ结构域之一的已知关联来实现。我将免疫沉淀DSCAM/MAGI复合物，并通过质谱法鉴定其他蛋白质成分。我假设鉴定的蛋白质将分为两类：介导DSCAM细胞内信号传导的信号转导蛋白质，以及同时结合MAGIs的其他PDZ结构域的类似DSCAM的蛋白质，这些蛋白质也参与有关细胞类型的信息传递。这种多层次的方法将是阐明唐氏综合症等神经发育障碍的发病机制和一般发育神经生物学原理的有效手段。

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.