Trophic Interactions During Visual System Development

描述（由申请人提供）：Netrin-1是一种分泌型分子，在轴突引导过程中可作为引诱剂或排斥剂发挥作用。在视觉系统中，netrin参与了引导视神经轴突从眼睛中向大脑中的目标移动。我们的长期目标是阐明控制视网膜和其中央目标之间的适当连接的发展的调节机制。在这里，我们建议测试的假设，netrin-1是牵连在视网膜发育的后期方面，显着影响视觉功能。具体来说，我们的目标是证明：1）netrin-1，通过对特定受体亚型的独立信号传导，影响视网膜轴突在目标和他们的突触后神经元在大脑中，和2）适当的视网膜顶盖布线需要netrin和脑源性神经营养因子（BDNF），调节突触发生的营养因子之间的功能相互作用。我们将这些假设建立在以下观察结果的基础上：i）netrin在视网膜轴突寻路期之后影响视网膜轴突，ii）在结直肠癌（DCC）中缺失的两种netrin受体和β-5在视网膜顶盖发育期间以互补模式表达，iii）BDNF和netrin共享共同的信号传导机制以影响轴突引导。实时成像实验和netrin信号的空间和时间控制的操作将在活爪蟾蝌蚪检查netrin在视觉系统发育中的作用。待检验的具体假设为：1. Netrin-1通过DCC受体激活，指导视网膜轴突终止并形成视神经轴突乔木结构和突触连接。操纵netrin水平和DCC信号在视顶盖内将被用来分析netrin的轴突靶向，分支和突触前位点分化的作用。2. Netrin-1通过β-5受体信号传导影响突触后顶盖神经元的形态和突触发育。体内成像实验将用于确定netrin是否参与早期树突发生，控制先驱树突过程的方向，以及netrin是否调节树突分支和突触后部位分化。3. Netrin和BDNF在功能上相互作用以形成视网膜顶盖突触连接。分子和体内成像研究将检查通过DCC受体的netrin信号传导是否是BDNF调节视网膜轴突分支和突触发生的上游。BDNF拯救受DCC信号改变影响的视网膜轴突的能力也将被测试。总的来说，拟议的研究将揭示netrin-1是视网膜顶盖回路发育的关键参与者，并将进一步加深我们对控制视觉通路发育的机制的理解，这对维持正常的视觉功能至关重要。

DESCRIPTION (provided by applicant): Netrin-1 is a secreted molecule that can function as either an attractant or repellent during axon guidance. In the visual system, netrin has been implicated in the guidance of optic axons out of the eye towards their targets in the brain. Our long-term goal is to elucidate the regulatory mechanisms controlling the development of proper connections between the retina and its central targets. Here, we propose to test the hypothesis that netrin-1 is implicated in late aspects of retinotectal development that significantly impact visual function. Specifically, we aim to demonstrate that; 1) netrin-1, through independent signaling on specific receptor subtypes, influences retinal axons at the target and their postsynaptic neurons in the brain, and 2) proper retinotectal wiring requires functional interactions between netrin and brain-derived neurotrophic factor (BDNF), a trophic factor that modulates synaptogenesis. We base these hypotheses on the observations that; i) netrin influences retinal axons past the period of retinal axon pathfinding, ii) the two netrin receptors deleted-in-colorectal cancer (DCC) and UNC-5 are expressed in complementary patterns during retinotectal development and, iii) BDNF and netrin share common signaling mechanisms to influence axon guidance. Real-time imaging experiments and spatially and temporally controlled manipulations in netrin signaling will be performed in living Xenopus tadpoles to examine netrin's role in visual system development. The specific hypotheses to be tested are: 1. Netrin-1, through DCC receptor activation, instructs retinal axons where to terminate and shapes optic axon arbor structure and synaptic connectivity. Manipulations in netrin levels and DCC signaling within the optic tectum will be used to analyze the role of netrin in axon targeting, branching, and presynaptic site differentiation. 2. Netrin-1, through UNC-5 receptor signaling, influences the morphological and synaptic development of postsynaptic tectal neurons. In vivo imaging experiments will be used to establish whether netrin participates in early dendritogenesis, controlling the orientation of pioneer dendritic processes and whether netrin modulates dendritic branching and postsynaptic site differentiation. 3. Netrin and BDNF interact functionally to shape retinotectal synaptic connectivity. Molecular and in vivo imaging studies will examine if netrin signaling through DCC receptors is upstream of BDNF regulation of retinal axon branching and synaptogenesis. The ability of BDNF to rescue retinal axons affected by altered DCC signaling will also be tested. Collectively, the proposed studies will reveal that netrin-1 is a key player in retinotectal circuit development and will further our understanding of the mechanisms that control the development of visual pathways, that are critically important in the maintenance of normal visual function.