Pathfinding and target recognition by cortical axons

我们建议研究的机制，控制不同阶段的发展皮层第5层和第6层传出投射到脑干和脊髓，包括他们的寻路和分子控制他们的识别和神经支配的目标。我们将通过制造发育不良的亚板轴突或完全缺乏亚板神经元的转基因小鼠，并通过分析不能形成丘脑皮质投射的Mash-1突变小鼠，来验证这一假设，即皮层亚板轴突通过这条路径进入和离开皮层的主要路径的开创性。为了测试轴突化学引诱物Netrin-1在分子上定义了通过前脑、中脑和后脑的第5层皮质脊髓轴突的皮质下路径的想法，我们将该轴突路径与Netrin-1表达的模式相关联，并将分析Netrin-1或其受体DCC缺陷的突变小鼠的皮质脊髓轴突异常寻路。其余的目标集中在皮质脊髓轴突的靶识别，其特征在于沿着轴突轴沿着从头形成分支并定向生长成靶。我们将研究BMP-3和一种新的分泌型CAM样蛋白的作用，该蛋白具有6个IG结构域和一个MAM结构域（暂时命名为“Ig 6 M”），其是使用差异显示PCR筛选分离的，以鉴定皮质脊髓轴突的候选靶识别分子。我们将使用体外轴突引导和分支测定，以及小鼠功能获得和功能丧失遗传实验，以确定BMP-3和Ig 6 M在控制皮质脊髓轴突分支的形成和定向生长中的充分性和需求。

We propose to study the mechanisms that control distinct phases of the development of cortical layer 5 and layer 6 efferent projections to the brainstem and spinal cord, including their pathfinding and the molecular control of their recognition and innervation of targets. We will test the hypothesis that the pioneering of the major path in and out of the cortex by cortical subplate axons through this path. This will be done by creating transgenic mice engineered to have stunted subplate axons, or lack subplate neurons altogether, and by analyzing Mash-1 mutant mice that fail to form a thalamocortical projection. To test the idea that the axonal chemoattractant, Netrin-1, molecularly defines the subcortical path of layer 5 corticospinal axons through the forebrain, midbrain and hindbrain, we will correlate this axonal path with the pattern of Netrin-1 expression, and will analyze mutant mice deficient for Netrin-1 or its receptor, DCC, for aberrant pathfinding by corticospinal axons. The remaining aims focus on target recognition by corticospinal axons, which is characterized by a de novo formation of branches along the axon shaft and their directed growth into targets. We will study the roles of BMP-3 and a novel secreted CAM-like protein with 6 Ig domains and a MAM domain (temporarily named "Ig6M"), which were isolated using a differential display PCR screen to identify candidate target recognition molecules for corticospinal axons. We will use in vitro axon guidance and branching assays, as well as gain-of-function and loss-of-function genetic experiments in mice, to determine the sufficiency and requirement of BMP-3 and Ig6M in controlling the formation and directed growth of corticospinal axon branches.