Mechanisms of Tangential Neuron Migration

描述（由申请人提供）：脊椎动物大脑中的几乎所有神经元都是“外来出生的”-也就是说，它们出生在心室表面或心室表面附近，然后迁移到另一个位置，在那里它们进行连接并执行其专门功能。神经元迁移可以是放射状的，平行于神经上皮的API-共基底轴，或者它们可以是 切向：垂直于顶-底轴-即，在神经上皮的平面上。为了探索定向神经元迁移的遗传调控机制，我们建立了面鳃神经元（FBMNs;颅神经VII）作为本实验室的模型系统，其经历了从后脑菱形节（r）4到r6的定型和进化保守的切线迁移。我们实验室和其他实验室的正向遗传学筛选已经确定了平面细胞极性（PCP）途径的多个核心组分对FBMN迁移至关重要。PCP途径被最好地理解为用于在上皮平面中的细胞之间产生和传递极性的细胞接触依赖性分子机制。然而，在发育和疾病状态期间，五氯苯酚与越来越多的细胞迁移有关。目前还没有关于PCP如何调节定向细胞迁移的连贯模型。这主要是因为定义PCP的极化细胞-细胞相互作用难以在细胞培养中重建，因此我们必须在体内解决这个问题。斑马鱼模型以其精致的活体成像、容易的转基因和强大的正向和反向遗传学工具为我们提供了这个机会。我们假设，在神经上皮的平面极化细胞和运动的FBMN之间的直接PCP信号传导使FBMN的迁移活性向迁移方向极化。我们建议首先通过识别迁移环境中负责指导迁移的细胞（目标1），然后通过阐明FBMN内的PCP信号如何影响其体内行为（目标2）来测试该模型的预测。此外，在目的2中，我们将发现迁移的FBMNs和周围神经上皮之间的相互作用如何影响PCP蛋白在FBMNs中的定位和迁移活性。最后，我们建议通过克隆我们在正向遗传筛选中确定的FBMN迁移突变体来丰富我们对PCP依赖的神经元迁移的理解（目的3）。

DESCRIPTION (provided by applicant): Almost all neurons in the vertebrate brain are "foreign born" - that is, they are born at or near the ventricular surface and then migrate to another location where they make their connections and carry out their specialized functions. Neuronal migrations can be radial, parallel to the api- co-basal axis of the neuroepithelium, or they can be tangential: orthogonal to the apical-basal axis - i.e., in the plane of the neuroepithelium. With te goal of discovering genetic mechanisms regulating directed neuronal migration, we have established the facial branchiomotor neurons (FBMNs; cranial nerve VII), which undergo a stereotyped and evolutionarily conserved tangen- tial migration from hindbrain rhombomere (r)4 to r6, as a model system in our lab. Forward ge- netic screens in our lab and others have identified multiple core components of the Planar Cell Polarity (PCP) pathway as being essential for FBMN migration. The PCP pathway is best under- stood as a cell contact-dependent molecular mechanism for generating and transmitting polarity between cells in the plane of an epithelium. However PCP has been implicated in a growing number of cell migrations during development and disease states. Currently no coherent model exists for how PCP regulates directional cell migration. This is mainly because the polarized cell- cell interactions that defin PCP are difficult to reconstitute in cell culture; we must therefore attack the problem in vivo. Th zebrafish model, with its exquisite live imaging, facile transgen- esis and powerful forward and reverse genetics tools, affords us this opportunity. We hypothe- size that direct PCP signaling between the planar-polarized cells of the neuroepithelium and the motile FBMNs polarizes FBMN protrusive activity in the direction of migration. We pro- pose to test the predictions of thi model first by identifying the cells in the migratory environ- ment that are responsible for directing migration (Aim 1), and then by elucidating how PCP sig- naling within the FBMNs affects their behavior in vivo (Aim 2). Furthermore in Aim 2 we will discover how interactions between migrating FBMNs and the surrounding neuroepithelium in- fluence PCP protein localization and protrusive activity in the FBMNs. Finally, we propose to enrich our understanding of PCP-dependent neuron migration through the cloning of FBMN migration mutants we have identified in a forward genetic screen (Aim 3).