Regulation of synaptic targeting in the Drosophila larval neuromuscular system by immunoglobulin superfamily cell surface proteins

项目总结/摘要 许多神经发育所必需的细胞表面蛋白（CSP）已经被鉴定出来，但我们仍然 缺乏对细胞间相互作用的逻辑的全面理解，这些细胞间相互作用对神经元的组装进行编程。 电路.我们的长期目标是了解由CSP介导的细胞间相互作用是如何编程的。 神经系统复杂突触模式的组装。多年前，有人提出，在“硬- 在“有线”系统如鱼的视顶盖和昆虫的CNS和神经肌肉系统中，每个神经元或 神经元类型由控制突触特异性的“识别标签”标记，并且这些标签是 由称为“表面标记”的特定CSP表示。最初的假设预测， 控制突触特异性应该是：1）在神经元或肌肉的小子集上表达，2）被 受体，其表达也仅限于小的神经元亚群（并且本身可能是表面的）。 标签），3）需要或影响特定突触连接的形成，4）由家族编码， 相关基因我们发现了一个满足所有这些标准的相互作用的CSP网络，使用一个新的 我们从全球体外相互作用网络中选择蛋白质进行体内分析。的 斯坦福大学的加西亚小组和我们在加州理工学院的小组为所有果蝇产生了一个细胞外“相互作用组 免疫球蛋白超家族（IgSF）蛋白，并发现了21个2-IG结构域细胞表面蛋白的亚家族， 选择性结合另一个3-IG结构域蛋白亚家族DIP的DIPs。每个dpr和DIP基因是 由一小部分独特的神经元表达，这些基因的突变会产生特定的改变， 在突触连接中。本申请的目的是定义是否以及如何交互 DIPs和DIPs之间的连接构成了一个“连接代码”，有助于果蝇中的布线特异性 幼虫神经肌肉系统本申请的主要假设是， 与它们的DIP伙伴提供可以控制突触靶向决定的信息。我们计划实现 通过三个具体目标实现本申请的目标。其中第一个研究了Dpr-DIP相互作用 控制特定运动神经元轴突分支的形成。第二个分析了另一个DIP 在单个运动神经元上表达的基因控制其肌肉靶的神经支配。第三种是创建工具， 分析所有的DIPs和DIP，并确定那些由特定的运动神经元和肌肉表达。 拟议研究的预期成果将是获得对机制的新见解， 在一个相对简单的模型中，CSP之间的哪些相互作用控制突触连接的规范 系统这将对人类健康产生重大的积极影响， 涉及人类神经系统发育和疾病的保守机制。

PROJECT SUMMARY/ABSTRACT Many cell surface proteins (CSPs) that are essential for neural development have been identified, but we still lack an overall understanding of the logic of the cell-cell interactions that program the assembly of neural circuits. Our long-term goal is to understand how cell-cell interactions mediated by CSPs program the assembly of the intricate synaptic patterns of nervous systems. Many years ago, it was proposed that in “hard- wired” systems such as the fish optic tectum and the insect CNS and neuromuscular system, each neuron or neuronal type is labeled by “identification tags” that control synaptic specificity, and that these tags are represented by specific CSPs called “surface labels”. The original hypotheses predicted that surface labels that control synaptic specificity should be: 1) expressed on small subsets of neurons or muscles, 2) recognized by receptors whose expression is also restricted to small subsets of neurons (and might themselves be surface labels), 3) required for or influence the formation of specific synaptic connections, 4) encoded by families of related genes. We discovered a network of interacting CSPs that satisfies all of these criteria, using a new approach in which we selected proteins for in vivo analysis from a global in vitro interaction network. The Garcia group at Stanford and our group at Caltech generated an extracellular “interactome” for all Drosophila immunoglobulin superfamily (IgSF) proteins, and found a subfamily of 21 2-Ig domain cell-surface proteins, the Dprs, that selectively binds to another subfamily of 9 3-Ig domain proteins, the DIPs. Each dpr and DIP gene is expressed by a small and unique subset of neurons, and mutations in these genes produce specific alterations in synaptic connectivity. The objectives of the present application are to define whether and how interactions between Dprs and DIPs constitute a “connectivity code” that contributes to wiring specificity in the Drosophila larval neuromuscular system. The primary hypothesis underlying this application is that engagement of Dprs with their DIP partners provides information that can control synaptic targeting decisions. We plan to attain the objectives of this application through three specific aims. The first of these examines how Dpr-DIP interactions control formation of an axon branch of a specific motor neuron. The second analyzes how another DIP expressed on a single motor neuron controls innervation of its muscle target. The third creates tools for analysis of all Dprs and DIPs and identifies those expressed by specific motor neurons and muscles. The expected outcome of the proposed research will be the acquisition of new insights into the mechanisms by which interactions among CSPs control the specification of synaptic connections in a relatively simple model system. This will have a significant positive impact for human health by increasing our understanding of conserved mechanisms involved in nervous system development and disease in humans.