The function of alpha-spectrin in the Drosophila nervous system

在发育中的神经系统内，细胞极性在形成具有严格分离的膜域的树突和轴突的神经元细胞中最为明显。我们感兴趣的是细胞极性的作用，为发展中的胶质细胞。在果蝇中枢神经系统的中线胶质细胞显示出明显的初始顶-基底极性。在后期发育阶段，胶质细胞形成基底细胞突起，其向连合轴突迁移并伴随地缩回其顶端细胞突起。这种极性细胞组织在我们先前在表型筛选中鉴定的klötzchen突变体中受到干扰。Klötzchen未能补充α-血影蛋白，并且突变的Klötzchen表型可以通过使用泛素启动子表达aspectrin来拯救。此外，klötzchen突变体细胞克隆缺乏α-血影蛋白表达。然而，α-血影蛋白空表型不同于我们已经鉴定的8个独立的klötzchen等位基因的表型。此外，果蝇α-血影蛋白基因是不寻常的，因为它编码第二个基因在其第一个内含子，共享第一个非编码外显子与α-血影蛋白转录。在接下来的两年里，我们计划从分子水平上鉴定α-血影蛋白基因或内含子基因中的klötzchen突变。我们想解决的问题是，α-血影蛋白的损失如何导致极性神经胶质细胞表型的破坏。使用影响细胞极性的其他突变，我们将确定胶质细胞极性是否是后期分化/功能所必需的。除了进一步详细的表型分析，我们将进行α-血影蛋白的结构功能研究，以及我们将进行遗传筛选，旨在确定与klötzchen相互作用的基因。我们的实验将有助于了解α-血影蛋白如何调节细胞极性，以及这种极性如何为随后的胶质细胞功能所需。

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.