Mechanisms for cell-cell interactions to intiate 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， 维持正常的神经回路我们的长期目标是阐明细胞信号是如何 建立神经回路，以了解细胞通信如何转化为神经网络， 形态发生，并剖析神经回路组装中断如何可能导致 神经发育疾病。大脑发育的一个核心原则是， 形态发生需要由细胞内和细胞外基质介导的细胞骨架重塑的时空调节。 细胞外信号然而，虽然引导轴突生长的信号通路已经被发现， 虽然这些树突被广泛表征，但是将树突引导到它们的靶区的通路在很大程度上仍然不清楚， 由于树枝状分支的形态复杂且尺寸小，利用果蝇的ACC运动神经元， 它有一个高度定型的简单的树突模式和分子标记系统， 在复杂环境中的单个细胞，我们最近已经深入了解了 通过神经元间相互作用的树突发生。1)我们发现aCC和它的靶分子之间的相互作用 唐氏综合征细胞粘附分子（Down syndrome cell adhesion molecule，Dscam 1）介导了神经元（MP 1）的凋亡。2)Dscam 1受体 将Dreadlocks（Dock）衔接子蛋白和Pak 1激酶募集到aCC中的膜。3） 随后，Pak 1与活化的Cdc 42 GT3相互作用，导致细胞骨架重排。 接触部位。这些发现导致了一种新的模型，其中Dscam 1-Dock-Pak 1和Cdc 42途径 会聚以调节aCC树突发生。综合运用遗传学、生物化学和显微镜技术 技术，这个项目的目标是解决我们的理解枝晶规范的关键差距， 这个信号通路。在目的1中，为了确定分泌的配体Slit在介导Dscam 1中的潜在作用， 在aCC-MP 1接触位点的相互作用中，我们将研究一种名为Slit的糖蛋白是否有助于 在aCC和MP 1神经元上的Dscam 1受体之间的通信。在目标2中，阐明 Dscam 1相互作用导致胞质结构域中Y-磷酸化的机制，我们将 研究配体结合如何促进Dscam 1的酪氨酸磷酸化以刺激Dock结合。在Aim中 3，为了鉴定激活Cdc 42和aCC树突状细胞生成的上游信号，我们将检查是否存在激活Cdc 42和aCC树突状细胞生成的上游信号。 Ephrin受体通过Eh相互作用的鸟嘌呤核苷酸在aCC树突状细胞发生时激活Cdc 42 交换因子（Ephexin）。这些研究将为深入了解其分子机制提供重要的信息 中枢神经系统中的树突状细胞生成，这是一个非常未被探索的关键过程。从长远来看，这些研究 将为理解神经发育疾病的病因和潜在治疗提供基础。

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.