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

神经元是高度极化的细胞，具有称为轴突和树突的结构和功能不同的隔室。在胚胎和出生后早期发育期间，称为连合轴突的各种轴突将中枢神经系统的两个半部互连，用于左右神经元活动的适当整合和协调。 为了引导这些轴突的投射，它们的顶端有高度能动和敏感的结构，称为生长锥，它可以感知引导线索的梯度，并且可以被吸引到源或从源排斥开。许多引导分子已经被识别;然而，这些分子如何发出信号以提供轴突生长的方向控制仍然是未知的。越来越多的证据表明，一种称为平面细胞极性（PCP）信号传导的信号通路介导了这一过程。PCP是细胞在上皮平面中极化的过程。它包括一组必需基因，包括卷曲（Fz）和Vangl。这些基因的突变会导致神经管形成和连合轴突导向的缺陷。有人认为，除了PCP信号，导航生长锥可能依赖于更敏感的机制，涉及另一种极性称为顶部-基底极性途径（ABP）。ABP控制上皮细胞内的极性，并由许多基因介导，包括Par 3，Par 6和Scribble 1（Scrib 1）。 后者在神经管形成过程中与PCP基因Vangl 2在物理和遗传上相互作用。我们的项目旨在解剖ABP基因Scrib 1和PCP基因Vangl 2在连合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，在介导连合轴突的指导发展脊髓和前脑。我们接下来将确定在神经元培养物和切片中敲低Scrib 1或Vangl 2或Par 3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。我们还将确定直接作用于生长锥的Scrib 1的下游效应子，改变其结构以响应指导线索。在发育中的脊髓和大脑中连合轴突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，并将有助于剖析ABP基因Scrib 1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.************