A novel mechanism for synapse localization in the retina

项目摘要 神经回路的功能取决于不同类型突触的精确组织。在脊椎动物的视网膜中， 关键的计算是由微电路的并行网络执行的，这些微电路形成高度有序的系统， 局限于神经元不连续区域的突触。例如，视网膜无长突细胞整合， 计算输入，然后通过内部的突触将此信息传达给视网膜神经节细胞， 网状层（IPL）。虽然我们已经开始确定决定哪种类型的 突触应该形成，我们仍然知道很少关于突触的位置是如何控制的。我们的长期目标是 定义了突触定位的分子通路。这个探索性项目的具体目标是测试 新的假说认为，非典型钙粘蛋白Fat 3决定了突触的形成， 两种已知的突触发生分子WAVE调节复合物（WRC）和受体酪氨酸的活性 磷酸酶蛋白PTP δ。在这项工作过程中产生的数据将使我们能够更新我们的模型， 今后对这一途径进行更有重点的调查。 一些观察表明，脂肪3相互作用的WRC和PTP？来控制突触的定位， 视网膜。Fat 3属于一个非典型钙粘蛋白家族，在平面极性中具有已知的作用，平面极性是一种信号系统， 通过产生分子子域（5）在相邻细胞中产生并排列不对称性。Fat 3细胞内 结构域包含多种效应物的多个结合位点，包括已知的细胞骨架调节剂和突触调节剂。 组件，如WRC和PTPdelta。因此，Fat 3非常适合于响应相邻小区中的信号 然后诱导突触发育所需的适当细胞内反应。与这个想法相一致， 在fat 3突变小鼠中，视网膜无长突细胞显示出改变的迁移模式， 形成异位丛状层（4）。此外，通过创建和分析小鼠窝藏 通过对Fat 3-ICD不同区域的缺失，我们发现Fat 3对迁移和神经突收缩的影响可以 与其对突触发育的影响分开。重要的是，Fat 3依赖性突触发育 似乎特别依赖于与WRC和PTPdelta的相互作用。WRC是一个经过充分研究的监管机构， 肌动蛋白细胞骨架的局部变化，包括突触（12），而已知PTP δ对 神经系统其他部位的突触发育（13-15）。为了跟进这些观察结果，我们将使用 生物化学和遗传学方法的组合来表征Fat 3，WRC， 而PTP？测试野生型和fat 3突变小鼠视网膜突触发育是否需要WRC功能; 并通过检查单个和多个Fat 3和PTPdelta， 双突变小鼠品系。

PROJECT SUMMARY Neural circuit function depends on the precise organization of diverse types of synapses. In the vertebrate retina, key computations are performed by parallel networks of microcircuits that form highly ordered systems of synapses that are confined to discrete regions of neuropil. For instance, retinal amacrine cells integrate and compute inputs and then communicate this information to retinal ganglion cells via synapses in the inner plexiform layer (IPL). Although we have begun to identify the molecular mechanisms that dictate what type of synapse should form, we still know very little about how synaptic location is controlled. Our long term goal is to define a molecular pathway for synapse localization. The specific objective of this exploratory project is to test the new hypothesis that the atypical cadherin Fat3 determines where synapses will form by harnessing the activity of two known synaptogenic molecules, the WAVE Regulatory Complex (WRC) and the receptor tyrosine phosphatase protein PTPdelta. Data generated during the course of this work will allow us to update our model and develop a more focused investigation of this pathway in the future. Several observations suggest that Fat3 interacts with the WRC and PTP? to control synapse localization in the retina. Fat3 belongs to a family of atypical cadherins with known roles in planar polarity, a signaling system that creates and aligns asymmetries in neighboring cells by creating molecular subdomains (5). The Fat3 intracellular domain harbors multiple binding sites for diverse effectors, including known cytoskeletal regulators and synaptic components, such as the WRC and PTPdelta. Thus, Fat3 is well-suited to respond to signals in neighboring cells and then induce appropriate intracellular responses needed for synapse development. Consistent with this idea, in fat3 mutant mice, retinal amacrine cells show altered patterns of migration and retain extra processes outside of the IPL that go on to form an ectopic plexiform layer (4). Further, by creating and analyzing mice harboring deletions of various regions of the Fat3-ICD, we found that Fat3’s effects on migration and neurite retraction can be separated from its effects on synapse development. Importantly, Fat3-dependent synapse development appears to depend specifically on interactions with the WRC and PTPdelta. The WRC is a well-studied regulator of local changes to the actin cytoskeleton, including at the synapse (12), while PTPdelta is known to be important for synapse development elsewhere in the nervous system (13-15). To follow up on these observations, we will use a combination of biochemical and genetic approaches to characterize physical interactions among Fat3, WRC, and PTP?; test whether retinal synapse development in wild-type and fat3 mutant mice requires WRC function; and determine how Fat3 and PTPdelta influence each other’s distribution and function by examining single and double mutant mouse strains.