Molecular Mechanisms That Control Neuronal Positioning

产生神经元异位的遗传性疾病可能导致癫痫的发展，在极端情况下，还会导致严重的智力低下。我们的实验室研究神经元迁移的分子控制，目的是了解协调神经系统适当形成和功能所需的事件。通过对具有神经元定位缺陷的小鼠突变体的研究，促进了对神经元迁移调控机制的理解。对这些小鼠中缺陷基因的分析导致了对神经元迁移调控机制的深入了解。这个实验室专注于四个基因的产物，这些基因在共同的信号通路上共同作用，调节神经元的位置。这些蛋白质包括分泌蛋白Reelin，它通过细胞表面受体ApoER2和VLDLR诱导细胞质蛋白Dab1的酪氨酸磷酸化。受这一级联反应调控的Dab1酪氨酸磷酸化位点已被证明是Dab1功能和正常大脑发育所必需的。因此，我们集中精力鉴定与Dab1以酪氨酸磷酸化依赖的方式相互作用的蛋白质。最近，我们已经确定Nckβ就是这样一种蛋白质。在培养的成纤维细胞中，我们已经证明了Dab1和Nckβ的共同过表达导致了肌动蛋白细胞骨架的变化。作为对Reelin刺激的响应，NCKβ从细胞体转移到细胞过程中，在那里它可能起到调节细胞骨架动力学的作用。我们目前正在分析其他Dab1结合蛋白，以确定它们是否受Reelin信号调节。这一途径的组成部分继续在成年动物中表达。因此，除了分析这种级联反应在大脑形成中的作用外，我们还在研究这种信号级联反应在维持神经系统功能方面的作用。目前正在使用Dab1的条件等位基因来研究这一点，该等位基因在出生后将在一部分神经元中失活。

Genetic disorders that produce neuronal ectopias can result in the development of epilepsy or, in extreme cases, severe mental retardation. Our lab studies the molecular controls of neuronal migration with the goal of understanding the events that are required to orchestrate the appropriate formation and function of the nervous system. Understanding of the mechanisms regulating neuronal migration has been facilitated by studies on mouse mutants that have neuronal positioning defects. Analyses of the defective genes in these mice have led to insights about the mechanisms regulating neuronal migration. This lab focuses on the products of four genes that work together on a common signaling pathway to regulate neuronal placement. These proteins include the secreted protein, Reelin, that acts through the cell surface receptors ApoER2 and VLDLR to induce the tyrosine phosphorylation of a cytoplasmic protein Dab1. The Dab1 tyrosine phosphorylation sites that are regulated by this cascade have been shown genetically to be required for Dab1 function and normal brain development. We have therefore concentrated our efforts on identifying and characterizing proteins that interact with Dab1 in a tyrosine phosphorylation dependent manner. Recently, we have identified Nck beta as one such protein. In cultured fibroblasts, we have demonstrated that co-overexpression of Dab1 and Nck beta leads to alterations in the actin cytoskeleton. In response to Reelin stimulation, Nck beta translocates from the cell soma into cellular processes where it may act to regulate cytoskeletal dynamics. We are currently analyzing other Dab1 binding proteins to determine if they are regulated by Reelin signaling. The components of this pathway continue to be expressed in adult animals. Therefore, in addition to analyzing a role for this cascade in the formation of the brain, we are also investigating a role for this signaling cascade in the maintenance of nervous system function. This is being investigated using a conditional allele for Dab1, which shall be inactivated in a subset of neurons postnatally.