Recognition Molecules in Cortical Development

描述(申请人提供)：CHL1(L1的Close Homolog)是一种与L1细胞黏附分子相关的整合素相互作用的细胞识别分子，在新皮质的区域特异性发育中具有潜在的作用。人类CHL1基因的突变(CALL)与智力低下的3P综合征有关。在径向迁移的皮质前体细胞和分化的锥体神经元中，CHL1表达于高尾端到低吻端的梯度。初步结果显示，CHL1基因敲除小鼠表现出锥体细胞的径向迁移和顶端树突投射的区域和板层特异性异常，以及丘脑皮质轴突的地形图错误。 有待检验的假设是，CHL1调节小鼠新皮质中皮质神经元的径向迁移，从而影响树突投射和丘脑皮质映射。目的：(1)明确CHL1基因敲除纯合子和杂合子小鼠皮质神经元的面积和板层特异性分布及其树突发育，并在双突变小鼠中评估CHL1和L1的相互作用。将在脑片上研究CHL1在Semaphorin 3A诱导的锥体神经元树突投射和分支中的作用。(2)通过体内BrdU标记和延时视频显微镜脑片分析，探讨CHL1在新皮质后皮质神经元径向迁移中的细胞机制。(3)探讨CHL1通过与黏附动力学有关的中间产物(Src、Rac、Pak、ERK1、2)参与细胞内信号转导的分子机制。(4)用轴突示踪法在体内识别CHL1-/-小鼠丘脑皮质投射的地形图缺陷，并通过胚胎轴突示踪法和端脑整体挂载法分析CHL1在丘脑轴突导引中的作用。 这项研究可以揭示控制大脑皮层发育的新的分子决定因素和新的机制，并为了解与智力低下相关的病理提供洞察力。

DESCRIPTION (provided by applicant): CHL1 (Close Homolog of L1) is an integrin-interacting cell recognition molecule related to the L1 cell adhesion molecule with a potential role in area-specific development of the neocortex. Mutation of the CHL1 gene (CALL) in humans is associated with the 3p-syndrome of mental retardation. CHL1 is expressed in a high caudal to low rostral gradient in cortical precursors during radial migration and in differentiating pyramidal neurons. Preliminary results show CHL1 knockout mice exhibit area- and lamina-specific abnormalities in radial migration and apical dendrite projection of pyramidal cells, and topographic mapping errors of thalamocortical axons. The hypothesis to be tested is that CHL1 modulates radial migration of cortical neurons in the mouse neocortex with consequences on dendrite projection and thalamocortical mapping. Aims are: (1) To define the area- and lamina-specific distribution of cortical neurons and their dendritic development in homozygous and heterozygous CHL1 knockout mice and to assess the interaction of CHL1 with L1 in double mutant mice. A role for CHL1 in Semaphorin 3A-induced dendritic projection and branching of pyramidal neurons will be studied in cortical slices. (2) To determine the cellular mechanism of CHL1 in radial migration of cortical neurons in the posterior neocortex by BrdU labeling in vivo and in brain slice assays by time lapse videomicroscopy. (3) To investigate the molecular mechanism of CHL1 in intracellular signaling through intermediates (Src, Rac, Pak, ERK1,2) important for adhesion dynamics. (4) To identify topographic mapping defects in the thalamocortical projection of CHL1-/- mice by axon tracing in vivo and to analyze CHL1 function in thalamic axon guidance by axon tracing in embryos and a novel telencephalic whole mount assay. This investigation can reveal new molecular determinants and novel mechanisms governing cortical area development and provide insight into the pathology associated with mental retardation.