The Role of LKB1 in the Specification of Neuronal Polarity

描述（申请人提供）：神经元极性对大脑正常发育至关重要，但在分子水平上对树突和轴突极化生长的机制知之甚少。了解神经元连接模式的机制对于理解它们在神经系统功能和功能障碍中的作用至关重要。本研究旨在确定新皮层锥体神经元树突/轴突生长极性的关键分子机制。我们最近进行了研究，以确定在皮层发育过程中指定神经元极性的基因。一个候选分子是LKB1（也称为Par4），这是一种丝氨酸-苏氨酸激酶，在无脊椎动物和哺乳动物上皮细胞中是一种牢固建立的细胞极性调节剂。LKB1的缺失会导致被称为Peutz-Jeghers的癌症易感性综合征。通过在发育中的小鼠皮质中条件缺失LKB1表达，我们发现LKB1是轴突起始所必需的，并且LKB1的过度激活可以诱导发育中的锥体神经元细胞体细胞中出现多个轴突。我们建议使用结构/功能方法来确定启动轴突生长所需的LKB1结构域（目的1）。LKB1有几种确定的底物，其中许多与细胞极性的建立有关。然后，我们将在体外和体内使用功能增益和功能丧失方法，以确定哪些下游效应物对LKB1指定神经元极性至关重要（目的2）。最后，将结合延时成像和细胞极性的活荧光报告来确定何时何地需要LKB1，以确定发育中的皮质神经元的轴突极性（目的3）。

DESCRIPTION (provided by applicant): Neuronal polarity is critical to proper brain development, but the mechanisms underlying the polarized outgrowth of dendrites and axons remain poorly understood at the molecular level. Understanding the mechanisms patterning neuronal connections is essential to understanding their roles in nervous system function and dysfunction. This proposal aims to identify a critical molecular mechanism specifying the polarity of dendrite/axon growth of pyramidal neurons in the neocortex. We have recently undertaken studies to identify genes specifying neuronal polarity during cortical development. One candidate molecule is LKB1 (also called Par4), a serine-threonine kinase that is a firmly established regulator of cell polarity in invertebrates and mammalian epithelial cells. Loss of LKB1 leads to the cancer predisposition syndrome known as Peutz-Jeghers. Using conditional deletion of LKB1 expression in the developing mouse cortex, we found that LKB1 is required for axon initiation and that over-activation of LKB1 can induce the emergence of multiple axons from the cell soma in developing pyramidal neurons. We propose to use a structure/function approach in order to identify the domains of LKB1 required for initiating axon outgrowth (Aim 1). LKB1 has several identified substrates, many of which are implicated in the establishment of cell polarity. We will then use both gain- and loss-of-function approaches in vitro and in vivo in order to determine which downstream effectors are critical in order for LKB1 to specify neuronal polarity (Aim 2). Finally, combination of time-lapse imaging and live fluorescent reporters of cell polarity will be used to identify when and where LKB1 is required in order to specify axonal polarity of developing cortical neurons (Aim 3).