A novel mechanism for synapse localization in the retina

项目总结 神经回路的功能依赖于不同类型突触的精确组织。在脊椎动物的视网膜中 关键计算由形成高度有序的系统的微电路的并行网络来执行 仅限于神经纤维束的离散区域的突触。例如，视网膜无长突细胞整合和 计算输入，然后通过内部的突触将这些信息传递给视网膜神经节细胞 网状层(IPL)。尽管我们已经开始确定决定哪种类型的 突触应该形成，但我们仍然对突触的位置如何控制知之甚少。我们的长期目标是 确定突触定位的分子途径。这个探索性项目的具体目标是测试 关于非典型钙粘附素Fat3决定突触形成位置的新假设是通过利用 波形调节复合体(WRC)和受体酪氨酸这两个已知突触生成分子的活性 磷酸酶蛋白PTPDelta。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和 在未来对这一途径进行更有针对性的研究。 一些观察表明，Fat3与WRC和PTP？控制突触在脑内的定位 视网膜。Fat3属于一个非典型钙粘附素家族，在平面极性中具有已知的作用，是一种信号系统， 通过创建分子亚域来创建和排列相邻细胞中的不对称性(5)。细胞内的Fat3 结构域包含多种效应器的多个结合位点，包括已知的细胞骨架调节因子和突触 部件，如WRC和PTPDelta。因此，Fat3非常适合对相邻细胞中的信号做出反应 然后诱导突触发育所需的适当的细胞内反应。与这个想法一致的是， 在FAT3突变小鼠中，视网膜无长突细胞显示了改变的迁移模式，并保留了额外的外部突起 形成异位丛状层的IPL(4)。此外，通过创建和分析窝藏在 通过对Fat3-ICD不同区域的缺失，我们发现Fat3的S效应可以影响轴突的迁移和回缩 脱离其对突触发育的影响。重要的是，Fat3依赖的突触发育 似乎具体取决于与WRC和PTPDelta的互动。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PTPDelta已知对 神经系统其他部位的突触发育(13-15)。为了跟进这些观察，我们将使用 生物化学和遗传学方法的结合来表征Fat3，WRC， 以及PTP？；测试野生型和FAT3突变小鼠的视网膜突触发育是否需要WRC功能； 确定Fat3和PTPDelta是如何影响彼此的分布和功能的 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.