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，疾病相关脑回路中的突触传递异常可能导致神经精神疾病的病因。因此，一个基本的问题是：如何指定和维护电路级突触属性？在分子上，突触细胞粘附分子（SCAM）是主要候选者，因为它们通常跨越突触前膜和突触后膜，物理连接两个末端并启动细胞内信号级联以将关键突触分子募集到突触。此外，基因组研究发现，许多与精神疾病相关的分子发生了突变。neurexin-3（Nrxn 3）是一种重要的突触前SCAM，其独特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相关，并且由于腹侧下托（vSub）-丘脑核（NAc）壳回路中的过度活跃而共享多巴胺失调的共同病理生理学基础。该回路的过度活跃可由vSUB-NAc投射回路或腹侧下托局部回路中的突触传递的变化引起。尽管vSUB-NAc壳电路的重要性显而易见，但缺乏对该电路的分子和突触理解。因此，neurexin-3发挥关键的，细胞类型特异性和非冗余的功能，以形成投影和局部脑托电路，多巴胺调节是必不可少的假设将在本提案中进行测试。目的1将研究Nrxn 3是如何被支配NAc壳中表达D1 R或D2 R的MSNs的两种类型的VEP投射神经元利用的。一个基本的理解之间的细胞类型的特定连接的vapor和NAc壳和Nrxn 3如何塑造这些兴奋性突触特性是未开发的;因此，解剖这种疾病电路内的细胞类型特定的前和突触后功能的下托神经元可能会打开新的途径的治疗策略。目的2将建立在K99训练阶段产生的初步RNA-seq数据的基础上，该数据显示Nrxn 3亚型表达在海马GABA能中间神经元的两个不同子集中受到强烈差异调节。我们将解剖知之甚少的细胞类型特定的本地电路在下托和离散Nrxn 3基因产物是如何利用形状细胞类型特定的突触传递。目的3将使用单细胞RNA-seq方法表征下托中电生理学上不同的锥体神经元的转录谱。这种无偏的方法将允许鉴别差异的、细胞类型特异性的疾病相关的SCAM表达，用于未来的研究，并用于产生遗传工具以促进下托的解剖。Nrxn 3在局部和投射下托回路中的分子询问将首次深入了解neurexin-3的疾病相关性，并将进一步了解neurexin的一般功能，并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.