Mechanisms Underlying Type II Cadherin Guided Assembly of Retinal Circuits

在眼睛里，复杂的视网膜回路连接在一起，进行精确的神经计算。多样但精确的 中间神经元和视网膜神经节细胞之间的连线是神经元回路处理的结构基础。 不同的视觉特征。这些并联电路的接线是精确的，因为有缺陷可能会导致几只眼睛。 疾病和神经系统疾病。为了研究不同类型的神经元 精确地整合到不同的平行视网膜回路中，我们开发了一种方法， 访问独特的开关方向选择电路，它传达方向选择性信号，作为理想的 模型系统我们先前的研究现在使我们能够检查II型钙粘蛋白（Cdhs）在 以单个蛋白质或组合的形式组装这个电路。我们发现两个Cdh，Cdh 9和Cdh 8， 指示平行的ON和OFF双极电池输入到ON-OFF方向选择性的ON与OFF子层 电路，从而允许精确分离的ON和OFF通道。然而，分子机制 这一集会的根本原因仍然难以捉摸。为了研究这种差异的分子机制， Cdh 9与Cdh 8的功能，我们将进行一系列的解剖和功能分析。我们将确定 钙粘蛋白分子的特定部分，细胞外与细胞内结构域，负责 它们独特的功能，以及它们在双极细胞之间形成突触的特定时间 和神经节细胞。我们还发现，来自双极神经元的Cdh 9异嗜性地识别来自突触后指向ON-OFF方向选择性神经节细胞的两个密切相关的Cdh，Cdh 6和Cdh 10 （ooDSGCs）和星爆状无长突细胞（SAC）。我们将利用这个已建立的遗传系统来揭示 组合Cdh一起作用以连接并行的方向选择电路。我们将从基因上进行研究， Cdh 6 -9-10单、双和三重组合在功能上如何模式化α 1-ooDSGC相互作用 在SAC。为了进一步扩大我们对神经元模式化中的组合钙粘蛋白编码的理解，我们 将测试Cdh 11的作用，Cdh 11通过分子生物学鉴定为鼻指向ooDSGC富集基因， 侧写因此，我们将产生新的分子和遗传靶向方法来检查的作用， Cdh 11及其密切相关的Cdh 8在鼻指向方向选择回路的布线中的作用而且我们 建立了子宫内注射系统，以异位地将单独的II型Cdh引入到鼻-ooDSGCs或鼻-ooDSGCs上，以在调节DS-回路图案化中精确定位组合Cdh。总的来说， 我们的研究试图揭示Cdh组合如何控制平行但不同的DS电路的形成。 对II型Cdh功能的全面研究将是一个长期存在的问题的重大进展， 哺乳动物的神经发育这些研究将是理解多重 基因相互作用来指定复杂神经回路的线路。所确定的机制将具有重大意义 与整个中枢神经系统的选择性电路布线有关。

In the eye, complex retinal circuits are wired together for precise neural computation. The diverse but precise wiring between interneurons and retinal ganglion cells serve as the structural basis for circuit processing of different visual features. These parallel circuits are wired up precisely, as defects may lead to several eye diseases and neurological disorders. To investigate the mechanisms behind how diverse neuronal types precisely integrate into distinct parallel retinal circuits, we developed methods that allow for targeted genetic access of the unique On-Off direction-selective circuit, which conveys direction-selectivity signals, as the ideal model system. Our previous studies now position us to examine the role of Type II Cadherins (Cdhs) in assembling this circuit as individual proteins or in combinations. We showed that two Cdhs, Cdh9 and Cdh8, instruct parallel ON and OFF bipolar cell input to ON vs. OFF sublaminae of the ON-OFF direction-selective circuit, thus allowing precise segregation of ON and OFF channels. However, the molecular mechanisms underlying this assembly remain elusive. To investigate the molecular mechanisms underlying the differential functions of Cdh9 vs. Cdh8, we will perform a series of anatomical and functional analyses. We will identify the specific portion of the cadherin molecule, extracellular versus intracellular domains, that are responsible for their distinct functions, as well as the specific timing of their actions in forming synapses between bipolar cells and ganglion cells. We also found that Cdh9 from bipolar neurons heterophilically recognizes the two closely-related Cdhs, Cdh6 and Cdh10, from postsynaptic Ventral-pointing ON-OFF direction-selective ganglion cells (ooDSGCs) and starburst amacrine cells (SACs). We will use this established genetic system to reveal how combinatorial Cdhs act together to wire up parallel direction-selective circuits. We will examine genetically and functionally how Cdh6-9-10 single, double, and triple combinations pattern the Ventral-ooDSGC interaction with SACs. To further expand our understanding of the combinatorial cadherin code in neuronal patterning, we will test the role of Cdh11, which is identified as a Nasal-pointing ooDSGC enriched gene through molecular profiling. Thus, we will generate new molecularly and genetically targeted methods to examine the roles of Cdh11 and its closely related Cdh8 in the wiring of Nasal-pointing direction-selective circuits. Furthermore, we established an in utero injection system to ectopically introduce individual Type II Cdhs onto Ventral-ooDSGCs or Nasal-ooDSGCs to pinpoint combinatorial Cdhs in regulating DS-circuit patterning. Collectively, our studies seek to reveal how Cdh combinations control the formation of parallel but distinct DS circuits. Comprehensive studies on Type II Cdh function would be a major advance for a long-standing question in mammalian neural development. These studies will be a major step forward in understanding how multiple genes interact to specify the wiring of complex neural circuits. The identified mechanisms will have significant relevance to selective circuit wiring throughout the central nervous system.