Genetic analysis of chandelier cells during cortical circuit assembly

描述（由申请人提供）：在哺乳动物大脑皮层中，GABA能抑制性中间神经元调节神经回路的功能组织。抑制性中间神经元由具有不同形态、连接模式和生理特性的不同类别组成。皮质中间神经元的刻板性和特异性表明其构建和组装中存在严格的遗传程序。了解GABA中间神经元的发育对于获得关于组装皮层回路的连贯知识是必要的。虽然在理解皮层中间神经元的早期发育方面取得了很大进展，从它们在腹侧端脑中的产生到它们长距离迁移到皮层中，但仍然不清楚不同类别的中间神经元是如何被指定并传递到适当的皮层区域和层的。此外，人们对中间神经元如何整合到皮层回路中知之甚少。一个关键的障碍是缺乏方法和策略，可以跟踪任何明确定义的中间神经元类别的发育历史，从它们的起源到它们整合到皮层回路。我们已经进行了系统的遗传方法，以靶向主要类别的皮质中间神经元。特别是，我们已经从遗传学上捕获了枝形吊灯细胞（CHCs），这是最独特的一类皮质中间神经元，专门支配轴突起始段（动作电位产生的部位）的锥体细胞。因此，CHC可能是对锥体细胞放电施加决定性控制的最强大的皮质神经元，从而动态地配置神经系综。然而，目前对社区卫生服务的了解很少，其起源和发展几乎完全未知。由于其特殊的刻板性和特异性，CHCs的遗传捕获为研究其整个发育历史建立了一个强大的实验范式。我们将研究CHCs的三个发展里程碑：起源，定居到特定的皮质层，并在电路集成大规模修剪。利用基因工程、命运作图、体内成像和电生理学，我们将实现对这些关键事件的高分辨率描述，并开始探索潜在的分子机制。我们的目标是建立一个基于细胞类型的实验范式，将纵向整合的关键发展步骤，在更大的背景下，使CHCs和整合到皮层电路。CHC中的缺陷与几种脑部疾病如癫痫和精神分裂症有关。CHCs的遗传分析不仅将提供一个关键的切入点，了解新皮层电路的组装，但也将揭示神经精神疾病的致病机制，并提出新的治疗策略。

DESCRIPTION (provided by applicant): In mammalian cerebral cortex, GABAergic inhibitory interneurons regulate the functional organization of neural circuitry. Inhibitory interneurons consist of diverse classes with distinct morphology, connectivity patterns, and physiological properties. The stereotypy and specificity in cortical interneurons suggest stringent genetic programs in their construction and assembly. Understanding the development of GABA interneurons is necessary to gaining a coherent knowledge on the assembly cortical circuits. Although much progress has made in understanding the early development of cortical interneurons, from their generation in the ventral telencephalon to their long distance migration into the cortex, it is still unclear how distinct classes of interneuron are specified and delivered to appropriate cortical areas and layers. Furthermore, little is known about how interneurons are integrated into cortical circuitry. A key obstacle is the lack of method and strategy that allow the developmental history of any well-defined class of interneurons to be tracked from their origin to their integration into cortical circuits. We have undertaken a systematic genetic approach to target major classes of cortical interneurons. In particular, we have genetically captured chandelier cells (CHCs), the most distinctive class of cortical interneurons that exclusively innervate pyramidal cells at axon initial segments, the site of action potential generation. CHCs are thus likely the most powerful cortical neurons that exert decisive control over pyramidal cell firing, thereby dynamically configure neural ensembles. However, current knowledge on CHCs is poor, and their origin and development are almost entirely unknown. Because of their exceptional stereotypy and specificity, genetic capture of CHCs establishes a powerful experimental paradigm for studying their entire developmental history. We will examine three developmental milestones of CHCs: origin, settlement into specific cortical lamina, and massive pruning during circuit integration. Using genetic engineering, fate mapping, in vivo imaging, and electrophysiology, we will achieve a high resolution description of these key events, and begin to explore the underlying molecular mechanisms. We aim to establish a cell type-based experimental paradigm that will longitudinally integrate key developmental steps in the larger context of making and integrating CHCs into cortical circuits. Deficiencies in CHCs have been implicated in several brain disorders such as epilepsy and schizophrenia. Genetic analysis of CHCs not only will provide a key entry point to understanding the assembly of neocortical circuitry but also will shed light into the pathogenic mechanisms of neuropsychiatric disorders and suggest new strategies for therapy.