Regulation of astroglial branch morphogenesis during visual circuit assembly in Drosophila

在我们的大脑中，神经元通常与不同的神经胶质亚型密切合作。星形胶质细胞在控制神经回路的发育、功能和稳态中起着至关重要的作用。尽管星形胶质细胞的数量和大小与大脑大小和认知能力相关，但它们在脊椎动物和无脊椎动物的神经系统中都具有非常复杂的形态，具有包裹细胞体、神经元轴突和树突的面纱状突起。虽然所有星形胶质细胞具有共同的核心生理特性，但它们在不同的大脑区域具有不同的形态。在揭示控制神经元形态和连通性的分子机制方面取得了很大进展。然而，星形胶质细胞如何获得其独特形状的基本问题很少受到关注，迄今为止，只有有限数量的决定因素被确定在这一重要的生物学过程中发挥作用。果蝇黑腹果蝇是一种强大的模式生物，用于确定细胞和组织中已知或新基因的功能。考虑到遗传功能的高度进化守恒，在果蝇中获得的见解与包括人类在内的哺乳动物的研究高度相关。在这项研究中，我们利用果蝇的视觉系统来揭示星形胶质细胞样胶质细胞正确分支形态发生所需的基因。先前，我们已经确定了一种星形细胞样胶质亚型，具有典型的细柱状和分层过程，非常适合于发育过程中的功能遗传学研究。我们发现了一种新的富含亮氨酸的跨膜重复结构域，它包含细胞表面分子，称为Lapsyn，它是胶质分支延伸到突触神经节所必需的。本提案中概述的研究旨在深入了解Lapsyn如何在分子上起作用，以加深我们对胶质分支形态发生的了解。基于我们早期的遗传研究，我们假设Lapsyn控制星形细胞样胶质细胞分支的延伸，以响应神经元膜结合或分泌决定因素。初步数据表明，在星形胶质细胞样胶质细胞中，Lapsyn可能不作为受体，而是作为共受体或结构细胞表面蛋白，通过其他细胞表面分子与细胞骨架调节剂和复合物中的组分相互作用。因此，我们旨在以公正的方式确定Lapsyn的上游和下游结合伙伴，并详细表征它们的功能。此外，为了加强我们对星形胶质细胞样胶质细胞正确分支延伸对神经元连接和功能的重要性的理解，我们将研究分支延伸与突触形成之间的联系，并评估它们在回路活动中的参与。从长远来看，这些对正常星形胶质细胞发育的见解将促进我们对星形胶质细胞特异性遗传对人类神经发育和神经退行性疾病的理解。

Within our brains, neurons generally exist in a close partnership with different glial subtypes. Astrocytes play a critical role in controlling neural circuit development, function and homeostasis. Although the number and size of astrocytes correlates with brain size and cognitive abilities, they adopt remarkably complex morphologies with veil-like processes that ensheath the cell bodies and axonal and dendritic arborizations of neurons in both vertebrate and invertebrate nervous systems. While all astrocytes have common core physiological properties, they constitute a heterogeneous population with distinct morphologies in different brain regions. Much progress has been made in uncovering the molecular mechanisms that control neuronal morphology and connectivity. However, the fundamental question how astrocytes acquire their distinct shapes has received little attention and only a limited number of determinants has so far been identified to play a role in this important biological process.The fruit fly Drosophila melanogaster is a powerful model organism for determining the function of known or novel genes in cells and tissues of interest. Considering the high degree of evolutionary conservation of genetic functions, insights gained in Drosophila are highly relevant for studies in mammals, including humans. In this study, we use the visual system of Drosophila to uncover the genes required for correct branch morphogenesis of astrocyte-like glia. Previously, we have identified an astrocyte-like glial subtype with stereotypic fine columnar and layered processes that is well suited for functional genetic studies during development. We have found a novel transmembrane Leucine-rich repeat domain containing cell surface molecule, called Lapsyn, that is essential for glial branch extension into the synaptic neuropil. Outlined research in this proposal seeks to gain insights how Lapsyn functions molecularly to deepen our knowledge of glial branch morphogenesis. Based on our earlier genetic studies we hypothesize that Lapsyn controls branch extension of astrocyte-like glia in response to neuronal membrane-bound or secreted determinants. Preliminary data suggest that in astrocyte-like glia, Lapsyn likely does not function as a receptor but as a co-receptor or structural cell surface proteins which interact with cytoskeletal regulators and components in a complex via other cell surface molecules. We therefore aim to identify the upstream and downstream binding partners of Lapsyn in an unbiased manner and to characterize their function in detail. Furthermore, to enhance our understanding of the significance of correct branch extension of astrocyte-like glia for neuronal connectivity and function, we will examine the link between branch extension and synapse formation and assess their participation in circuit activity. At long term, these insights into normal astrocyte development will advance our understanding of astrocyte-specific genetic contributions to neurodevelopmental and neurodegenerative disorders in humans.