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

神经元是高度极化的细胞，在结构和功能上各有不同的隔间，称为轴突和树突。不同的轴突称为连合轴突，在胚胎和出生后早期发育期间，将中枢神经系统的两半相互连接，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，它们的顶端有高度运动和敏感的结构，称为生长锥体，可以感知引导线索的梯度，可以被吸引到来源，也可以远离来源。许多引导分子已经被确定；然而，这些分子如何发出信号来提供轴突生长的定向控制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)的信号通路参与了这一过程。PCP是细胞在上皮平面内极化的过程。它包括一组必要的基因，包括FrizzledFz和Vangl。这些基因的突变会导致神经管形成和连合轴突引导的缺陷。有人提出，除了PCP信号外，导航生长锥可能依赖于更敏感的机制，涉及另一种称为尖端-基底极性途径(ABP)的极性。ABP控制着上皮细胞内的极性，并受许多基因的调节，包括Par3、Par6和Scribble1(Scrib1)。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在连合轴突引导过程中的分子联系。我们将研究这两个基因在调节发育中的脊髓和前脑的连合轴突引导中的相互作用。接下来，我们将确定在神经元培养和切片中敲除Scrib1或Vangl2或Par3是否会影响神经元的极性、PCP介导的轴突生长以及各种ABP和PCP标记的亚细胞定位。我们还将确定Scrib1的下游效应器，这些效应器直接作用于生长锥体，根据指导提示改变其结构。 在发育中的脊髓和大脑中的连合轴突引导仍然是一个有趣的现象。我们的研究将对这一基本的发育过程提供重要的见解，并有助于剖析ABP基因Scrib1和PCP信号在调节这一过程中的作用。

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.