Regulation of axon formation by Rab10 and Arhgef7

神经元是高度极化的细胞，在分子和功能上建立不同的轴突和躯体-树突间隔。新生有丝分裂后神经元最初表现为具有多个未分化突起的多极形态。他们通过选择其中一个轴突作为轴突来建立他们的极化形态。在啮齿动物胚胎大脑的海马神经元培养中，神经元极化自发发生，而不需要模式外部信号的输入。轴突的伸展依赖于生长锥中特化的质膜前体小泡(PPV)的胞吐而使质膜扩张。它是通过细胞内运输进入新生的轴突的极化来促进的，新生的轴突为生长提供了物质。PPV在极化前存在于所有轴突中，但它们的胞吐作用优先发生在新生轴突的生长锥体中。轴突的形成是由调节细胞骨架动力学以及细胞内运输和胞吐的GTP酶调控的。PPV的特征是存在GTPase Rab10，该酶在未极化的神经元的所有神经元突起中都可检测到，但极化后在轴突中变得丰富。Rab10对于轴突的形成是必不可少的，它的敲除可以防止神经元极化。在胞吐之前，PPV被八聚体胞囊复合体拴在生长锥的质膜上，八聚体胞囊复合体对轴突的形成至关重要。外囊复合体被GTPase TC10募集到膜上。我们已经确定Arhgef7是一种在轴突形成过程中激活TC10的环境基金。当Arhgef7被基因敲除或敲除失活时，神经元无法延伸轴突。在这个项目中，我们将研究Rab10GEF、Rab10和Argef7在PPV在轴突形成过程中的运输和胞吐中的作用。

Neurons are highly polarized cells that establish molecularly and functionally distinct axonal and somato-dendritic compartments. Newborn postmitotic neurons initially exhibit a multi-polar morphology with several undifferentiated processes. They establish their polarized morphology by selecting one of their neurites as the axon. Neuronal polarization happens spontaneously in cultures of hippocampal neurons from the embryonic brain of rodents without requiring an input from patterned extrinsic signals. Axon extension depends the expansion of the plasma membrane by the exocytosis of specialized plasmalemma precursor vesicles (PPVs) in the growth cone. It is facilitated by the polarization of intracellular transport into the nascent axon that provides the material for growth. PPVs are present in all neurites before polarization but their exocytosis occurs preferentially in the growth cone of the nascent axon. The formation of axons is orchestrated by GTPases that regulate cytoskeletal dynamics as well as intracellular transport and exocytosis. PPVs are characterized by the presence of the GTPase Rab10 that is detectable in all neurites of unpolarized neurons but becomes enriched in the axon upon polarization. Rab10 is essential for axon formation and its knockdown prevents neuronal polarization. Prior to their exocytosis, PPVs are tethered at the plasma membrane of the growth cone by the octameric exocyst complex that is essential for axon formation. The exocyst complex is recruited to the membrane by the GTPase TC10. We have identified Arhgef7 as a GEF that activates TC10 during axon formation. When Arhgef7 is inactivated by a knockout or a knockdown, neurons fail to extend axons. In this project we will investigate the role of Rab10 GEFs, Rab10 and Argef7 for the trafficking and exocytosis of PPVs during axon formation.