Genetic analysis of chandelier cells during cortical circuit assembly

描述（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不同的种类组成，具有不同的形态、连接模式和生理特性。皮层中间神经元的刻板性和特异性表明它们的构建和组装有严格的遗传程序。了解GABA中间神经元的发育是获得对组装皮层回路的连贯认识的必要条件。尽管在理解皮层中间神经元的早期发育方面已经取得了很大进展，从它们在腹侧端脑的产生到它们长距离迁移到皮层，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，对于中间神经元如何整合到皮层回路中，我们所知甚少。一个关键的障碍是缺乏方法和策略来追踪任何一类明确定义的中间神经元的发育历史，从它们的起源到它们与皮层回路的整合。我们已经采取了系统的遗传方法来针对主要类别的皮层中间神经元。特别是，我们从基因上捕获了枝形细胞（CHCs），这是最独特的一类皮质中间神经元，专门支配轴突初始节的锥体细胞，这是动作电位产生的部位。因此，chc可能是最强大的皮质神经元，对锥体细胞的放电施加决定性的控制，从而动态地配置神经系统。然而，目前对CHCs的了解很少，其起源和发展几乎完全未知。由于其特殊的刻板印象和特异性，CHCs的基因捕获为研究其整个发展史建立了强有力的实验范式。我们将研究CHCs的三个发展里程碑：起源，沉降到特定的皮层层，以及电路整合过程中的大量修剪。利用基因工程、命运图谱、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种基于细胞类型的实验模式，在更大的背景下，将CHCs制造和整合到皮层回路中，纵向整合关键的发育步骤。CHCs的缺乏与癫痫和精神分裂症等几种脑部疾病有关。CHCs的遗传分析不仅将为理解新皮质回路的组装提供关键切入点，而且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.