Genetic control of chandelier interneuron specification in cerebral cortex

描述(申请人提供)：大脑皮层内的神经元放电活动由各种抑制性GABA能中间神经元调节，这些神经元能够通过大量的形态、分子、突触和电生理特性微调电路活动。内在的遗传程序和外在的经验驱动的学习都可能在定义不同的神经元亚型，并以适当的密度将这些细胞分布到整个大脑的层和区域以允许形成有意义的电路主题方面发挥作用。为了全面了解中间神经元的发育，下一个挑战是描述一个真正的中间神经元亚型的整个生活史，例如枝形吊灯细胞，可以说是迄今为止描述的最独特和最统一的GABA能中间神经元。枝形吊灯细胞有一个明确的轴突树枝，由数百个垂直排列的盒状突触组成，每个突触特定地支配锥体细胞的轴突起始部分，也就是产生动作电位的部位。一个枝形吊灯细胞可以迅速影响关键皮质层中大群兴奋细胞的放电，而精神分裂症患者大脑中枝形吊灯细胞外周的特异性缺陷，进一步突显了它们的重要性。我们最近鉴定了小鼠枝形吊灯细胞的空间和时间起源，证明这些细胞起源于以前未被描述的与侧脑室接壤的区域，我们称之为腹侧生发区(VGZ)。这项提议的目标是发现祖细胞遗传程序和出生时间对大脑皮层关键区域枝形吊灯细胞分布和规格的影响。我们建议将依赖cre的报告与发育转录因子的可诱导敲入cre驱动相结合，以便在体内将枝形吊灯细胞定位于发育中的啮齿动物大脑中的杏仁核、新皮质和海马体。此外，我们建议在遗传交叉策略中结合cre和flppase系，以具有前所未有的时间特异性的放射状神经胶质干细胞和中间前体细胞的神经元生成细胞分裂为靶点。这些实验将在“出生”时有效地标记枝形吊灯细胞，并允许跟踪它们进入皮质的轨迹，在那里它们被组装成特定的皮质层。在发育过程中，前体细胞分裂的时间和位置是精心安排的，这是一个重要的过程，为神经元-锥体细胞间突触的形成奠定了基础。理想情况下，这些方法将提供一个无与伦比的例子，说明特定类型的神经元是如何产生的，并适当地分配到皮质，以便整合到神经元电路中。通过研究这些事件，我们希望开始了解神经连接障碍最终是如何在精神分裂症中表现为衰弱的认知和行为障碍的，精神分裂症是一种疾病，困扰着超过1%的普通人口。

DESCRIPTION (provided by applicant): Neuronal firing activity within the cerebral cortex is regulated by a diverse assortment of inhibitory GABAergic interneurons, which are able to finely tune circuit activity through a vast array of morphological, molecular, synaptic, and electrophysiological properties. Intrinsic genetic programs and extrinsic experience- driven learning are both likely to play a role in defining different neuronal subtypes and distributing these cells to layers and regions throughout the brain in the proper density to allow formation of meaningful circuit motifs. To approach a complete understanding of interneuron development, the next challenge is to characterize the entire life history of a bona-fide interneuron subtype such as the chandelier cell, arguably the most distinct and uniform GABAergic interneuron yet to be described. Chandelier cells have an unmistakable axon arbor of hundreds of vertically arranged cartridge synapses, each of which specifically innervates the axon initial segment of a pyramidal cell, the site where action potentials are generated. A single chandelier cell can rapidly impact the firing of large groups of excitatory cells in critical cortical layers, while spcific deficits in chandelier cell boutons occur in the brains of schizophrenia patients, further highlighting their importance. We recently characterized the spatial and temporal origin of chandelier cells in mice, demonstrating that these cells originate in a previously uncharacterized domain bordering the lateral ventricle that we have termed the ventral germinal zone (VGZ). The goal of this proposal is to discover the impact of progenitor cell genetic programs and birth timing on chandelier cell distribution and specification in key regions of the cerebral cortex. We propose to combine cre-dependent reporters with inducible knock-in cre drivers of developmental transcription factors in order to fate map chandelier cells to the amygdala, neocortex, and hippocampus in the developing rodent brain in vivo. Furthermore, we propose to combine cre and flippase lines in genetic intersectional strategies to target neuron-generating cell divisions of radial glial stem cells and intermediate progenitor cells with unprecedented temporal specificity. These experiments will effectively mark chandelier cells at the time of "birth" and allow the tracking of their trajectory into the cortex, where they are assembled into specific cortical layers. The timing and location of progenitor cell divisions are carefully orchestrated during development, an important process that sets the stage for interneuron-pyramidal cell synapse formation. These approaches will ideally provide an unparalleled example of how a specific type of neuron is produced and appropriately dispatched into the cortex for integration into neuronal circuitry. By studying these events, we hope to begin to understand how disordered neuronal connectivity ultimately manifests as debilitating cognitive and behavioral disturbances in schizophrenia, an illness that afflicts more than 1% of the general population.