Mechanisms for Cell-Cell Interactions to Initiate Dendrite Outgrowth

单个神经元的轴突、树突和突触必须定位在适当的靶点上，以建立 并维持起作用的神经回路。我们的长期目标是阐明细胞信号如何 建立神经回路，以了解细胞通信如何转化为神经 形态发生，并剖析神经回路组装的破坏如何导致 神经发育疾病。大脑发育的一个核心原则是电路组装和神经 形态发生需要通过细胞内和细胞外信号调节细胞骨架重塑的时空调节 细胞外信号。然而，尽管引导轴突生长的信号通路一直是 广泛描述的是，将树枝引导到其目标区域的路径仍然不清楚，在很大程度上 由于树枝形态复杂，尺寸较小。利用果蝇ACC运动神经元， 它具有高度刻板的、简单的树枝状图案，以及允许检查的分子标记系统 对于复杂环境中的单个细胞，我们最近深入了解了 神经元间相互作用的树突发生。1)我们发现ACC与其靶点之间的相互作用 神经元(MP1)由唐氏综合征细胞黏附分子(Dscam1)介导。2)Dscam1受体 在ACC的膜上招募Dock(Dock)适配蛋白和Ak1激酶。3) 随后，pak1与激活的cdc42 GTP酶相互作用，导致细胞骨架重排 联系地点。这些发现导致了一个新的模型，在该模型中，Dscam1-Dock-pak1和CDC42通路 融合以调控ACC树突状细胞的发生。使用遗传学、生物化学和显微技术的组合 技术，这个项目的目标是通过以下方式解决我们对枝晶规范理解中的关键差距 这条信号通路。在目标1中，确定分泌配体狭缝在介导Dscam1中的潜在作用 在ACC-MP1接触位点的相互作用，我们将检查一种名为Sit的糖蛋白是否促进 ACC上的Dscam1受体与MP1神经元之间的通讯。在目标2中，阐明 Dscam1相互作用导致细胞质区域Y-磷酸化的机制，我们将 研究配体结合如何促进Dscam1的酪氨酸磷酸化以刺激Dock结合。在AIM 3，为了确定激活CDC42和ACC树突发生的上游信号，我们将检查 肾上腺素受体通过与肾上腺皮质激素相互作用的鸟嘌呤核苷酸在ACC树突状细胞发生时激活CDC42 交换因子(Ephexin)。拟议中的研究将为分子机制提供重要的见解。 在中枢神经系统中，树突发生的一个关键过程被极大地低估了。从长远来看，这些研究 将为了解神经发育疾病的病因和潜在的治疗方法提供基础。

The axons, dendrites, and synapses of individual neurons must be positioned at appropriate targets to establish and maintain functional neural circuits. Our long-term goals are to elucidate how cellular signaling establishes neural circuits, to understand how cellular communication translates into neural morphogenesis, and to dissect how disruption of neural circuit assembly may result in impairments in neurodevelopmental disease. A core principle in brain development is that circuit assembly and neural morphogenesis require spatiotemporal regulation of cytoskeletal remodeling mediated by both intracellular and extracellular signaling. However, while the signaling pathways that guide axonal outgrowth have been extensively characterized, the pathways that direct dendrites into their target fields remain obscure, in large part due to the complicated morphology and small size of dendritic branches. Using the Drosophila aCC motoneuron, which has a highly stereotyped, simple dendrite pattern, and molecular marker systems that allow examination of individual cells in complex environments, we have recently gained insight into the specification of dendritogenesis by inter-neuronal interactions. 1) We found that interaction between the aCC and its target neuron (MP1) is mediated by Down syndrome cell adhesion molecule (Dscam1). 2) The Dscam1 receptor recruits the Dreadlocks (Dock) adapter protein and the Pak1 kinase to the membrane in the aCC. 3) Subsequently, Pak1 interacts with activated Cdc42 GTPase, leading to cytoskeletal rearrangements at the contact site. These findings have led to a novel model in which the Dscam1-Dock-Pak1 and the Cdc42 pathways converge to regulate aCC dendritogenesis. Using a combination of genetics, biochemistry and microscopy techniques, the objective of this project is to address key gaps in our understanding of dendrite specification by this signaling pathway. In Aim 1, to define the potential role of the secreted ligand Slit in mediating Dscam1 interactions at the aCC-MP1 contact site, we will examine whether a glycoprotein called Slit facilitates communication between Dscam1 receptors on the aCC and the MP1 neurons. In Aim 2, to elucidate the mechanism by which Dscam1 interactions lead to Y-phosphorylation in the cytoplasmic domain, we will investigate how ligand binding promotes tyrosine phosphorylation of Dscam1 to stimulate Dock binding. In Aim 3, to identify upstream signaling that activates Cdc42 and aCC dendritogenesis, we will examine whether the Ephrin receptor activates Cdc42 at the onset of aCC dendritogenesis via an Eph-interacting guanine nucleotide exchange factor (Ephexin). The proposed studies will provide significant insights into the molecular mechanism of dendritogenesis in the CNS, a critical process that is greatly under-explored. In the long term, these studies will provide a foundation for understanding the etiology and potential treatment of neurodevelopmental diseases.