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，对患者及其家人的福祉构成重大负担。更好地了解神经元在正常和疾病状态下的发育将有助于一般生物学知识，也可能导致预防或治愈此类疾病。小鼠视觉系统是研究这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，通过研究视网膜神经元所学到的原理很可能普遍适用于大脑中的神经元。赞助商实验室最近的研究揭示了唐氏综合症细胞黏附分子(Dscam)和相关的Dscaml1基因(以下统称为Dscam)在小鼠视网膜内神经元自我回避中的作用。顾名思义，DSCAM发现于人类21号染色体与唐氏综合症有关的关键区间内。在没有DSCAM或DSCAML1的情况下，在正常表达DSCAM或DSCAML1的视网膜神经元亚群中可以看到特定类型的细胞聚集和树突束。在野生型眼睛中，这些神经元均匀分布，它们的轴突很少自我交叉。长期以来，人们一直认为视网膜神经元的间距和形态对于视觉信息的忠实处理很重要，Dscam突变小鼠代表了第一个直接检验这一假说的合适系统。在具体目标1中，我将使用已建立的机器人成像和非成像视觉的行为测试来评估DSCAM突变引起的解剖改变的功能后果。由于功能性突触仍在突变体中形成，而非成像视觉任务不太可能依赖地形图，因此我的假设如下：1)在特定行为所需的细胞类型(S)因DSCAM的丢失而中断的情况下，成像视觉将受到负面影响；2)非成像视觉将保持完好。来自视觉运动和瞳孔反应测试的初步数据支持这些假设。在具体目标2中，我将努力了解DSCAM功能的分子机制，并确定其他对神经元形态发生重要的蛋白质。这将通过利用DSCAM的C-末端与MAGIS的六个PDZ结构域之一(具有倒向结构域结构的膜相关鸟苷晚期激酶)之一的已知关联来实现。我将免疫沉淀DSCAM/MAGI复合体，并通过质谱学鉴定更多的蛋白质组分。我假设所鉴定的蛋白质将分为两类：介导DSCAM细胞内信号转导的蛋白质，以及与DSCAM类似的蛋白质，它们同时与MAGI的其他PDZ结构域结合，也参与细胞类型的信息交流。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发育的一般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.