Teneurin-3 and Latrophilin-2 in circuit-wide topographic target selection of the extended hippocampal network

项目摘要 中枢神经系统是由大量的神经元连接到电路，基础上的所有 大脑功能精确的电路组装部分是通过轴突靶选择完成的， 细胞表面分子（CSM），作为识别标签，以确定适当的突触伴侣。然而，在这方面， 一个健康的大脑所必须构建的突触的绝对数量超过了可用的数量， 编码基因的数量级。缓解这一挑战的一种方法是通过分子梯度， 连接是由一个分子的相对数量而不是单个分子来指定的。另一 是在不同的解剖区域重复使用相同的CSM。本提案的目标是利用 定型，拓扑连接的扩展海马网络，以检查是否有一个受体配体 CSM对可以介导功能电路的所有节点的精确组装。扩展海马网络 由CA1、下托（Sub）、内嗅皮层（EC）、乳头核（mMN）和 前腹侧丘脑（AVT）。每个节点进一步细分为平行的内侧和外侧海马 网络（分别为MHN和LHN）。到出生后第8天（P8），所有这五个区域都有反向梯度 CSMs的Teneurin-3（Teneurin-3）和Latrophilin-2（Lphn-2），分别限于MHN和LHN。这 互补表达式提出了"Ten3 → Ten3，Lphn2 → Lphn2"的连接规则。事实上，对于CA1 → Sub 投射，Ten3表达CA1轴突似乎被亚衍生Ten3吸引，并被亚衍生Ten3排斥。 Lphn2精确地靶向CA1的MHN细分。相反，表达Lphn2的CA1轴突被排斥， 以LHN为目标。全回路反转Ten3和Lphn2表达表明， 机制可以广泛地重复使用。这项提议将评估Ten3嗜同性的机制是否 吸引力和Ten3-Lphn2异嗜性排斥在每个解剖节点内重演。 扩展海马网络来调节精确的拓扑电路组装。使用组合 基因和病毒技术，Ten3或Lphn2将有条件地从每个起源和靶区域删除， 一系列功能丧失操作，然后进行病毒回路追踪以评估错误启动。本研究 代表介导整个功能性神经元的电路组装的单个受体-配体对的第一次测试。 网络线路中断是许多神经发育和精神疾病的标志，因此， 电路组装的分子机制可能导致与NIMH使命相关的治疗策略。 沿着本提案中的研究目标，该奖学金将支持额外的培训技术专长， 科学写作、指导和职业发展。斯坦福大学将提供理想的设备齐全， 智力多样性和协作环境，以完成拟议的研究。

PROJECT SUMMARY The central nervous system is made up a vast number of neurons connected into the circuits that underlie all brain function. Precise circuit assembly is accomplished, in part, through axonal target selection, mediated by cell surface molecules (CSMs) that serve as recognition tags to identify appropriate synaptic partners. However, the sheer volume of synapses that must be constructed for a healthy brain outstrips the number of available coding genes by orders of magnitude. One way to mitigate this challenge is through molecular gradients such that connections are specified by a relative amount of one molecule instead of by individual molecules. Another is to reuse the same CSMs in different anatomical regions. The goal of this proposal is to leverage the stereotyped, topographical connections of the extended hippocampal network to examine if one receptor-ligand CSM pair can mediate precise assembly of all nodes of a functional circuit. The extended hippocampal network consists of connections between CA1, subiculum (Sub), entorhinal cortex (EC), mammillary nucleus (mMN), and the anteroventral thalamus (AVT). Each node is further subdivided into parallel medial and lateral hippocampal networks (MHN and LHN, respectively). By postnatal day 8 (P8), all five of these regions have inverse gradients of the CSMs, Teneurin-3 (Ten-3) and Latrophilin-2 (Lphn-2), restricted to MHN and LHN, respectively. This complementary expression suggests a ‘Ten3→Ten3, Lphn2→Lphn2’ connectivity rule. In fact, for the CA1→Sub projection, Ten3-expressing CA1 axons appear to be attracted to Sub-derived Ten3 and repelled by Sub-derived Lphn2 to precisely target the MHN subdivision of CA1. Conversely, Lphn2-expressing CA1 axons are repelled by Sub-derived Ten3 to target the LHN. Circuit-wide inverse Ten3 and Lphn2 expression suggests these mechanisms could be reused broadly. This proposal will assess if the mechanisms of Ten3 homophilic attraction and Ten3-Lphn2 heterophilic repulsion are recapitulated at each anatomical node within the extended hippocampal network to mediate precise topographical circuit assembly. Using a combination of genetic and viral techniques, Ten3 or Lphn2 will be conditionally deleted from each origin and target region in a series of loss of function manipulations followed by viral circuit-tracing to assess mistargeting. This study represents the first test of a single receptor-ligand pair mediating the circuit assembly of an entire functional network. Disruption in wiring is a hallmark of many neurodevelopment and psychiatric disorders, so elucidating the molecular mechanisms of circuit assembly may lead to therapeutic strategies pertinent to the NIMH mission. Along with the research aims in this proposal, this fellowship will support additional training technical expertise, scientific writing, mentorship, and career development. Stanford University will provide the ideal well-equipped, intellectually diverse, and collaborative environment to complete the proposed study.