Molecular crosstalk between apical-basal polarity and planar cell polarity in axon guidance

神经元是高度极化的细胞，具有结构和功能上不同的室室，称为轴突和树突。在胚胎和出生后的早期发育阶段，被称为互交轴突的各种轴突相互连接中枢神经系统的两个半部分，以适当地整合和协调左右神经元的活动。为了引导这些轴突的投射，它们被称为生长锥的高度运动和敏感的结构所覆盖，这种结构可以感知引导信号的梯度，并可以被吸引到源或被排斥离开源。已经确定了许多引导分子；然而，这些分子信号是如何提供轴突生长方向控制的，在很大程度上仍然是未知的。越来越多的证据表明，一种称为平面细胞极性（PCP）信号通路介导了这一过程。PCP是细胞在上皮平面上极化的过程。它包含一组必需基因，包括卷曲（Fz）和Vangl。这些基因的突变导致神经管形成和交联轴突引导的缺陷。这表明，除了PCP信号外，生长锥的导航可能依赖于另一种更敏感的机制，即顶基极性通路（ABP）。ABP控制上皮细胞内的极性，并由包括Par3、Par6和Scribble1 （Scrib1）在内的许多基因介导。后者在神经管形成过程中与PCP基因Vangl2在物理和遗传上相互作用。我们的项目旨在剖析ABP基因Scrib1和PCP基因Vangl2在交联轴突引导过程中的分子联系。我们将研究这两个基因之间的相互作用，在发育中的脊髓和前脑的互交轴突指导中介导。接下来，我们将确定在神经元培养物和切片中敲低Scrib1或Vangl2或Par3是否会影响神经元极性、培养物中PCP介导的轴突生长以及各种ABP和PCP标记物的亚细胞定位。我们还将确定Scrib1的下游效应物，它们直接作用于生长锥，根据引导信号改变其结构。****在发育中的脊髓和大脑中，共同轴突的引导仍然是一个有趣的现象。我们的研究将为这一基本发育过程提供重要的见解，并将有助于解剖ABP基因Scrib1和PCP信号在介导这一过程中的作用。************

Neurons are highly polarized cells with structurally and functionally distinct compartments called axons and dendrites. Various axons called commissural axons interconnect the two halves of the central nervous system during embryonic and early postnatal developmental periods for proper integration and coordination of left-right neuronal activities. To guide these axons in their projections, they are tipped with highly motile and sensitive structures called the growth cones that perceive gradients of guidance cues and can be either attracted towards the source or repulsed away from it. Many guidance molecules have been identified; however, how these molecules signal to provide directional control of axon growth is still largely unknown. An increasing amount of evidence has implicated a signaling pathway called planar cell polarity (PCP) signaling in mediating this process. PCP is the process by which cells become polarized in the plane of an epithelium. It includes a group of essential genes including Frizzled (Fz) and Vangl. Mutations in these genes cause defects in neural tube formation and in commissural axon guidance. It was suggested that, in addition to PCP signaling, navigating growth cones might rely on more sensitive mechanisms implicating another kind of polarity called the apical-basal polarity pathway (ABP). ABP controls polarity within the epithelial cells and is mediated by many genes including Par3, Par6 and Scribble1 (Scrib1). The latter physically and genetically interacts with the PCP gene Vangl2 during neural tube formation. Our project aims at dissecting the molecular link between the ABP gene Scrib1 and the PCP gene Vangl2 during commissural axon guidance. We will investigate interactions between these two genes in mediating commissural axon guidance of the developing spinal cord and forebrain. We will next determine whether knockdown of Scrib1 or Vangl2 or Par3 in neuronal cultures and slices will affect neuronal polarity, PCP-mediated axonal growth in culture and subcellular localization of various ABP and PCP markers. We will also identify the downstream effectors of Scrib1 that act directly on the growth cone, changing its structure in response to guidance cues.****Commissural axon guidance in the developing spinal cord and brain remains an intriguing phenomenon. Our study will provide important insights into this fundamental developmental process and will help dissecting the role of the ABP gene Scrib1 and PCP signaling in mediating this process.************