The function of alpha-spectrin in the Drosophila nervous system

在发育中的神经系统中，细胞极性在神经元细胞中最为明显，它们形成具有严格分离的膜域的树突和轴突。我们对细胞极性在神经胶质细胞发育中的作用很感兴趣。在果蝇中枢神经系统中，中线胶质细胞表现出明显的初始顶基极性。在发育后期，胶质细胞形成基底细胞突起，向交联轴突迁移，并同时缩回其顶端细胞突起。这种极性细胞组织在klötzchen突变体中受到干扰，我们之前在表型筛选中发现了这种突变体。Klötzchen不能补充α -spectrin，突变体klötzchen表型可以通过使用泛素启动子表达aspectrin来挽救。此外，klötzchen突变细胞克隆缺乏α -spectrin的表达。然而，α -spectrin null表型不同于我们已经鉴定的8个独立klötzchen等位基因的表型。此外，果蝇α -幽灵蛋白基因是不寻常的，因为它在其第一个内含子内编码第二个基因，该内含子与α -幽灵蛋白转录本共享第一个非编码外显子。在接下来的两年里，我们建议在α -谱蛋白基因或内含子基因中分子鉴定klötzchen突变。我们想解决的问题是α -谱蛋白的损失如何导致极性胶质细胞表型的破坏。利用影响细胞极性的其他突变，我们将确定神经胶质细胞极性是否为后期分化/功能所必需。除了进一步详细的表型分析，我们将进行a-spectrin的结构功能研究，以及我们将进行基因筛选，旨在识别与klötzchen相互作用的基因。我们的实验将有助于理解α -谱蛋白是如何调节细胞极性的，以及这种极性是如何为后续的胶质细胞功能所必需的。

Within the developing nervous system cell polarity is mostly evident in neuronal cells which form dendrites and axons with strictly separate membrane domains. We are interested in the role of cell polarity for the developing glial cells. In the Drosophila CNS the midline glial cells show a pronounced initial apico-basal polarity. During later developmental stages, the glial cells form basal cell processes that migrate towards commissural axons and concomitantly retract their apical cell processes. This polar cell organization is disturbed in klötzchen mutants that we have previously identified in a phenotypic screen. Klötzchen fails to complement alpha-spectrin and the mutant klötzchen phenotype can be rescued by expression of aspectrin using the ubiquitin promoter. Furthermore, klötzchen mutant cell clones lack alpha-spectrin expression. However, the alpha-spectrin null phenotype differs from the phenotype of the 8 independent klötzchen alleles that we have identified. In addition, the Drosophila alpha-spectrin gene is unusual as it encodes a second gene within its first intron that shares the first noncoding exon with the alpha-spectrin transcript. In the next two years we propose to molecularly identify the klötzchen mutation in either the alpha-spectrin gene or the intron-based gene. We want to address the question how the loss of alpha-spectrin leads to a disruption of the polar glial cells phenotype. Using other mutations affecting cell polarity we will determine whether glial cell polarity is required for later differentiation / function. In addition to further detailed phenotypic analyses, we will perform structure function studies of a-spectrin as well as we will perform genetic screens aimed to identify genes interacting with klötzchen. Our experiments will contribute to the understanding how alpha-spectrin regulates cell polarity and how this polarity is required for subsequent glial cell function.