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伙伴的层流分布的分子机制，并确定获得投射神经元亚型特异性身份是否对与局部中间神经元的适当连接是必要的。这项工作旨在了解不同类型的投射神经元对平衡皮层微电路的建立的贡献。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令人惊讶的多样性的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，局部微电路的病变和/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电路中的发育事件尚不清楚。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，以及不同亚型的投射神经元独特而不同地决定不同类别的皮层中间神经元[4]的层流分布的准确性。我们发现Fezf2零突变小鼠的新皮层缺少脑下投射神经元，并被交联投射神经元取代，导致中间神经元异常层压和gaba能抑制改变。与此一致的是，靠近皮层的脑下投射神经元或胼胝体神经元的实验生成足以将皮质中间神经元招募到这些异位位置，并具有类别特异性。这些数据表明，投射神经元的个体群体以惊人的精度从外部控制着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”，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。在此，我们基于这一已发表的工作，以及我们最近的证明，有丝分裂后投射神经元的身份可以从一种亚型“重编程”到另一种体内[5]，以回答以下问题：1)是否存在一种“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能够指导中间神经元层压？涉及到什么分子？钙粘蛋白家族成员的“代码”是否参与建立适当的神经元间层压？（目标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电路/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随着投射神经元类别特异性身份的改变而改变？（目标3）我们提供了大量的已发表和试点数据来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.