Mechanisms of Tangential Neuron Migration

描述(申请人提供)：脊椎动物大脑中几乎所有的神经元都是“外来出生的”--也就是说，它们出生在脑室表面或靠近脑室表面，然后迁移到另一个位置，在那里它们建立联系并执行其特殊功能。神经元的迁移可以是放射状的，平行于神经上皮的api共同基底轴，也可以是 切向：与顶端-基底轴垂直--即在神经上皮平面内。为了发现调控神经元定向迁移的遗传机制，我们在实验室建立了面神经分支运动神经元(FBMN)作为我们实验室的一个模型系统，该神经元经历了一种刻板的、进化保守的从后脑菱形核到R6的切线迁移。我们实验室和其他实验室的前向磁屏已经确定平面细胞极性(PCP)途径的多个核心成分对FBMN的迁移是必不可少的。最好的理解是PCP途径是一种依赖于细胞接触的分子机制，用于在上皮平面上的细胞之间产生和传递极性。然而，PCP在发育和疾病状态下参与了越来越多的细胞迁移。目前还没有关于PCP如何调控细胞定向迁移的统一模型。这主要是因为定义PCP的极化细胞-细胞相互作用在细胞培养中很难重建；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、便捷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，在神经上皮平面极化的细胞和运动的FBMN之间直接PCP信号使FBMN向迁移方向的突起活动极化。我们建议首先通过识别迁移环境中负责指导迁移的细胞来检验这一模型的预测(目标1)，然后通过阐明FBMN中的PCP信号如何影响它们在体内的行为(目标2)。此外，在目标2中，我们将发现迁移的FBMN和周围的神经上皮之间的相互作用如何影响FBMN中PCP蛋白的定位和突起活性。最后，我们建议通过克隆我们在正向遗传筛选中发现的FBMN迁移突变体来丰富我们对PCP依赖的神经元迁移的理解(目标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).