Projection neuron control over interneuron positioning into neocortical circuitry

描述(申请人提供)：这项建议的目的是了解不同亚型的新皮质兴奋性投射神经元控制其中间神经元伙伴的层状分布的分子机制，并确定是否需要获得投射神经元亚型特定的身份才能与局部中间神经元正确连接。这项工作旨在了解不同类别的投射神经元对建立平衡的皮质微电路的贡献。包括认知、感觉知觉和运动功能在内的高级新皮质功能依赖于兴奋性投射神经元和抑制性中间神经元之间的局部微电路的协调组装。事实上，局部微回路的发育不良和/或功能障碍与癫痫、精神疾病和神经发育障碍有关[1-3]。支配投射神经元和中间神经元整合成平衡回路的发育事件知之甚少。我们已经报道了投射神经元在控制这一过程中所起的中心作用，以及不同类型的投射神经元唯一和不同地确定不同类别的皮质中间神经元的层状分布的精确度[4]。我们发现在Fezf2缺失突变小鼠的新皮质中没有大脑下投射神经元，而它们被连合投射神经元取代，导致中间神经元的异常层叠和GABA能抑制的改变。一致的是，实验产生的大脑下投射神经元或靠近皮质的胼胝体神经元足以将皮质中间神经元招募到这些异位位置，具有类别特异性。数据表明，投射神经元的个体群体在细胞外以惊人的精度控制特定中间神经元类别的层流命运。这表明，在局部电路组装过程中，存在一种“分子密码”，它控制着投射神经元和中间神经元伙伴之间的特定相互作用。在这里，我们基于这项已发表的工作，以及我们最近的演示，即有丝分裂后投射神经元的身份可以在体内从一种亚型重新编程为另一种亚型[5]，以回答以下问题：1)是否存在允许投射神经元和中间神经元类别之间特定亚型的相互作用的“分子密码”来指导神经元间分层？所涉及的分子是什么？(目标1)2)钙粘蛋白家族成员的“密码”是否参与建立适当的神经元间层？(目标2)3)为了与神经元间伙伴建立平衡的电路/连接，是否有必要获得投射神经元亚型特定的身份？特定类别的中间神经元的抑制性输入是否会随着投射神经元类别特定身份的改变而改变？(目标3)我们提供了大量已公布的和试点的数据，支持这项工作的重要性和可行性。

DESCRIPTION (provided by applicant): The goal of this proposal is to understand the molecular mechanisms by which distinct subtypes of excitatory projection neurons of the neocortex govern the laminar distribution of their interneuron partners, and to define whether acquisition of projection neuron subtype-specific identity is necessary for proper connectivity with local interneurons. The work aims at understanding the contribution of different classes of projection neurons to the establishment of balanced cortical microcircuitry. High-level neocortical function including cognition, sensory perception and motor function relies on the coordinated assembly of a local microcircuitry among an astonishing diversity of excitatory projection neurons and inhibitory interneurons. Indeed, disgenesis and/or disfunction of the local microcircuitry is associated with epilepsy, psychiatric disease and neurodevelopmental disorders [1-3]. The developmental events governing the integration of projection neurons and interneurons into balanced circuitry are poorly understood. We have reported on the central role played by projection neurons in governing this process and the precision by which different subtypes of projection neurons uniquely and differentially determine the laminar distribution of distinct classes of cortical interneurons [4]. We found that absence of subcerebral projection neurons from the neocortex of Fezf2 null-mutant mice and their replacement by commissural projection neurons cause abnormal lamination of interneurons and altered GABAergic inhibition. In agreement, experimental generation of either subcerebral projection neurons or callosal neurons in proximity to the cortex is sufficient to recruit cortical interneurons to these ectopic locations, with class-specificity. The data demonstrate that individual populations of projection neurons cell-extrinsically control the laminar fate of specific interneuron classes with striking precision. This suggests the existence of a "molecular code" that governs the specific interaction between projection neuron and interneuron partners during assembly of the local circuitry. Here, we build on this published work, as well as our recent demonstration that the identity of postmitotic projection neurons can be "reprogrammed" from one subtype into another in vivo [5] to answer the following questions: 1) Is there a "molecular code" enabling subtype-specific interactions among classes of projection neurons and interneurons to guide interneuron lamination? What are the molecules involved? (Aim 1) 2) Are "codes" of cadherin family members involved in establishing proper interneuron lamination? (Aim 2) 3) Is the acquisition of projection neuron subtype-specific identity necessary for the establishment of balanced circuitry/connectivity with interneuron partners? Does the inhibitory input by specific classes of interneurons change upon a change in projection neuron class-specific identity? (Aim 3) We present substantial published and pilot data supporting the significance and feasibility of this work.