Synaptic Dissection of Cell Adhesion Molecule Function within Subicular Circuits

描述（由申请人提供）：越来越多的证据表明，与疾病相关的脑回路中突触传递的异常可能导致神经精神疾病的病因。因此，关键的问题是：回路层面的突触特性是如何指定和维持的？从分子上讲，突触细胞粘附分子（SCAMs）是主要的候选者，因为它们通常跨越突触前和突触后膜，物理连接两个末端并启动细胞内信号级联，以招募关键的突触分子到突触。此外，基因组研究发现，许多与精神疾病相关的这些分子发生了突变。神经素-3 （Nrxn3）是一种重要的突触前诈骗，其特有的突变与人类精神分裂症（SZ）和药物成瘾有关。这些疾病与巨大的社会和经济负担有关，并有一个共同的病理生理基础，即由于腹侧下托(vSub) -伏隔核（NAc）壳回路过度活跃而导致多巴胺失调。该回路的过度活跃可由vSUB-NAc投射回路或腹侧枕下局部回路的突触传递变化引起。尽管vSUB-NAc外壳电路具有明显的重要性，但缺乏对该电路的分子和突触理解。因此，神经素-3在形成多巴胺调节所必需的投射和局部丘下电路中发挥关键的、细胞类型特异性和非冗余功能的假设将在本提案中得到验证。目的1将研究Nrxn3如何被两种类型的vSUB投射神经元利用，这两种类型的vSUB投射神经元支配NAc壳中表达msn的D1R或D2R。对vSUB和NAc外壳之间细胞类型特异性连接的基本理解以及Nrxn3如何塑造这些兴奋性突触特性尚未探索；因此，在这种疾病回路中，解剖细胞类型特异性的隐下神经元突触前和突触后功能可能为治疗策略开辟新的途径。Aim 2将建立在K99训练阶段产生的初步RNA-seq数据的基础上，该数据揭示了Nrxn3亚型表达在海马gaba能中间神经元的两个不同亚群中受到强烈的差异调节。我们将剖析鲜为人知的枕骨下细胞类型特异性局部电路，以及如何利用离散的Nrxn3基因产物来塑造细胞类型特异性突触传递。目的3将利用单细胞RNA-seq方法表征枕下不同电生理锥体神经元的转录谱。这种无偏倚的方法将允许鉴别不同的，细胞类型特异性疾病相关的SCAM表达，用于未来的研究和遗传工具的生成，以促进耻骨下的解剖。Nrxn3在局部和突出的水下回路中的分子研究将首次深入了解neurexin-3的疾病相关性，并将进一步了解neurexin的总体功能，为未来的研究奠定基础。

DESCRIPTION (provided by applicant):Increasing evidence suggests that abnormalities in synaptic transmission in disease-relevant brain circuits likely contribute to the etiologies that underlie neuropsychiatric disorders. Thus, the essential question: how are circuit-level synaptic properties specified and maintained? Molecularly, synaptic cell adhesion molecules (SCAMs) are prime candidates because they often span the pre- and post-synaptic membrane, physically link both terminals and initiate intracellular signaling cascades to recruit key synaptic molecules to the synapse. Moreover, genomic studies have mutations in many of these molecules that are associated with psychiatric diseases. Mutations unique to neurexin-3 (Nrxn3), an essential presynaptic SCAM, have been linked to schizophrenia (SZ) and drug addiction in humans. These disorders are associated with an enormous social and economic burden and share a common pathophysiological basis of dopamine dysregulation due to hyperactivity in the ventral subiculum (vSub) - nucleus accumbens (NAc) shell circuit. Hyperactivity of this circuit can be caused by changes in synaptic transmission in the vSUB-NAc projection circuit or in the ventral subiculum local circuit. Despite the obvious importance of the vSUB-NAc shell circuit, a molecular and synaptic understanding of this circuit is lacking. Thus, the hypothesis that neurexin-3 plays critical, cell-type specific and nonredundant functions to shape projection and local subicular circuitry that are essential for dopamine regulation will be tested in this proposal. Aim 1 will investigate how Nrxn3 is utilized by the two types of vSUB projection neurons that innervate D1R or D2R expressing MSNs in the NAc shell. A fundamental understanding of the cell-type specific connectivity between the vSUB and NAc shell and how Nrxn3 shapes these excitatory synaptic properties is unexplored; thus, the dissection of cell-type specific pre- and post-synaptic functions of subicular neurons within this disease circuit may open new avenues for treatment strategies. Aim 2 will build on preliminary RNA-seq data generated during the K99 training phase that revealed Nrxn3 isoform expression is strongly differentially regulated in two distinct subsets of hippocampal GABAergic interneurons. We will dissect the poorly understood cell-type specific local circuit in the subiculum and how discrete Nrxn3 gene products are utilized to shape cell-type specific synaptic transmission. Aim 3 will characterize the transcriptional profiles of electrophysiologically distinct pyramidal neurons in the subiculum using a single-cell RNA-seq approach. This unbiased approach will allow for the identification of differential, cell-type specific disease-relevant SCAM expression for future study and for the generation of genetic tools to facilitate the dissection of the subiculum. The molecular interrogation of Nrxn3 in the local and projection subicular circuit will provide the first insight into the disease-relevance of neurexin-3 and will further our understanding of neurexin function in general and will lay the foundation for future studies.