Projection neuron control over interneuron positioning into neocortical circuitry

描述（由申请人提供）：本提案的目标是了解新皮层兴奋性投射神经元的不同亚型控制其中间神经元伴侣的层状分布的分子机制，并定义获得投射神经元亚型特异性身份是否是与局部中间神经元正确连接所必需的。这项工作的目的是了解不同类别的投射神经元建立平衡的皮层微电路的贡献。包括认知、感觉知觉和运动功能在内的高级新皮层功能依赖于兴奋性投射神经元和抑制性中间神经元的惊人多样性之间的局部微电路的协调组装。事实上，局部微电路的发育不全和/或功能障碍与癫痫、精神疾病和神经发育障碍有关[1-3]。控制投射神经元和中间神经元整合到平衡回路中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核心作用，以及不同亚型的投射神经元独特和差异地确定不同类别的皮层中间神经元的层状分布的精度[4]。我们发现Fezf 2缺失突变小鼠新皮层的大脑下投射神经元缺失，并被连合投射神经元替代，导致中间神经元层压异常，并改变GABA能抑制。在协议中，无论是大脑下投射神经元或胼胝体神经元在接近皮质的实验一代是足够的招募皮质interneurons到这些异位的位置，类特异性。这些数据表明，个别群体的投射神经元细胞外控制特定的interneuron类的层状命运惊人的精度。这表明存在一种“分子密码”，它控制着投射神经元和中间神经元在局部回路组装过程中的特定相互作用。在这里，我们建立在这个已发表的工作，以及我们最近的证明，有丝分裂后投射神经元的身份可以在体内从一种亚型“重编程”到另一种亚型[5]，以回答以下问题：1）是否有一个“分子密码”，使投射神经元和中间神经元之间的亚型特异性相互作用，以指导中间神经元分层？涉及哪些分子？(Aim 1）2）钙粘蛋白家族成员的“编码”是否参与建立适当的中间神经元分层？(Aim 2）3）获得投射神经元亚型特异性身份对于建立与中间神经元伙伴的平衡回路/连接是必要的吗？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异性身份的改变而改变？(Aim 3）我们提出了大量的已发表和试点数据，支持这项工作的意义和可行性。

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.