Inhibitors of Synaptogenesis and Mental Health

越来越多的证据表明，许多神经精神疾病都有一个发展的起源， 遗传基础大量的等位基因变异已被确定与精神疾病。 虽然基因发现是关键的第一步，但下一个重大挑战是定义生物化学 疾病等位基因改变的通路，并对这些功能失调的 通路破坏与疾病病理学相关的脑功能。令人感兴趣的是， 轴突导向分子的SEMAPHORIN（SEMA）家族及其受体，PLEXINS（PLXN）携带 精神疾病的遗传风险。SEMA 5A及其受体PLXNA 2的等位基因变体与 情绪障碍导致基因表达减少。为了探索生物学的基本原理， SEMA 5A/PLXNA 2表达可能与精神疾病有关，我们使用Plxna 2转基因小鼠作为研究对象。 实验系统Sema 5a和Plxna 2突变小鼠的形态学研究鉴定了不同的 解剖表型：早期出生的齿状颗粒细胞（GCs）祖细胞迁移缺陷， 初级神经上皮细胞的齿状回（DG）和脊髓突触密度的增加，在成熟的GC中， 的DG。成年Plxna 2小鼠在情景记忆中表现出基因剂量和性别特异性行为缺陷， 感觉运动门控和社交能力;精神疾病中常见的特征，包括 精神分裂症为了更深入地了解Plxna 2缺陷如何影响行为表型， 我们使用基因编辑来破坏PlxnA 2胞质区域中的GTP酶激活蛋白（GAP）结构域。 PlxnA 2-GAP酶活性的丧失损害Rap 1-GT3依赖性GC祖细胞迁移，并导致 成熟GC中的额外棘突触。此外，PlxnA 2-GAP缺陷会破坏情景记忆 和感觉运动门控为了更深入地探讨受损的Sema 5A/PlxnA 2-GAP/Rap 1信号传导如何导致 行为缺陷，我们使用了蛋白质组学为基础的方法，并确定了新的PlxnA 2相互作用蛋白。在 目前的应用，我们提出了一个多学科的方法，包括最近开发的生物化学 工具，电生理技术，条件基因消融和小鼠行为。具体目标1是 旨在表征调节Sema 5A-PlxnA 2信号传导的新机制，包括 拮抗PlxnA 2-GAP活性的鸟嘌呤核苷酸交换因子（GEF）。SPECIFIC AIM 2基于 我们观察到前脑特异性消融Plxna 2模拟了在Plxna 2中观察到的行为缺陷， 生殖细胞缺失小鼠。我们采用小鼠遗传学方法来确定脆弱性的发育时期 以及与Plxna 2-/-和Plxna 2-GAP缺陷小鼠中受损行为相关的神经底物。 遗传研究将辅之以电生理记录、组织学分析和高- 分辨率磁共振成像。研究旨在确定Plxna 2-GAP在何时何地 在大脑发育过程中，大脑的功能是确保成年后正常行为所必需的。

Mounting evidence suggests that many neuropsychiatric disorders have a developmental origin with a strong genetic underpinning. A large number of allelic variants has been identified that associate with mental illness. While genetic discoveries are a crucial first step, the next major challenge is to define the biochemical pathways altered by disease alleles and to develop a more nuanced understanding of how these dysfunctional pathways disrupt brain function relevant to disease symptomatology. Of interest, mutations in members of the SEMAPHORIN (SEMA) family of axon guidance molecules, and their receptors, the PLEXINS (PLXN) carry varying genetic risks for mental illness. Allelic variants of SEMA5A and its receptor PLXNA2 associated with mood disorders cause reduced gene expression. To explore the underlying biology of how reduced SEMA5A/PLXNA2 expression may contribute to mental illness, we use Plxna2 transgenic mice as an experimental system. Morphological studies with Sema5a and Plxna2 mutant mice identified distinct anatomical phenotypes: defects in migration of early-born dentate granule cells (GCs) progenitors from the primary neuroepithelium to the dentate gyrus (DG) and an increase in spine synapse density in mature GCs in the DG. Adult Plxna2 mice exhibit gene-dosage and sex-specific behavioral defects in episodic memory, sensorimotor gating, and sociability; traits commonly observed in psychiatric disorders including Schizophrenia. For a deeper understanding of how Plxna2 deficiency may contribute to behavioral phenotypes, we used gene editing to disrupt the GTPase-activating protein (GAP) domain in the PlxnA2 cytoplasmic region. Loss of PlxnA2-GAP enzymatic activity impairs Rap1-GTPase dependent GC progenitor migration and leads to supernumerary spine synapses in mature GC. Moreover, PlxnA2-GAP deficiency disrupts episodic memory and sensorimotor gating. To probe deeper into how impaired Sema5A/PlxnA2-GAP/Rap1 signaling leads to behavioral defects, we used a proteomics-based approach and identified novel PlxnA2 interacting proteins. In the current application we propose a multidisciplinary approach comprised of recently developed biochemical tools, electrophysiological techniques, conditional gene ablation and mouse behavior. SPECIFIC AIM 1 is aimed at the characterization of novel mechanisms that regulate Sema5A-PlxnA2 signaling, including the guanine nucleotide exchange factors (GEFs) that antagonize PlxnA2-GAP activity. SPECIFIC AIM 2 builds on our observation that forebrain specific ablation of Plxna2 mimics behavioral defects observed in Plxna2 germline null mice. We pursue a mouse genetic approach to identify developmental epochs of vulnerability and the neural substrate associated with impaired behaviors in Plxna2-/- and Plxna2-GAP deficient mice. Genetic studies will be complemented by electrophysiological recordings, histological analyses and high- resolution magnetic resonance imaging. Studies are aimed at determining where and when Plxna2-GAP function is required during brain development to ensure normal behavior in adulthood.