Laboratory of Cell and Neuronal Dynamics, Department of Biology, Faculty of Sciences, Universidad de Chile, 7800003, Santiago, Chile.
Geroscience Center for Brain Health and Metabolism, 7800003, Santiago, Chile.
J Neurosci. 2021 Feb 24;41(8):1636-1649. doi: 10.1523/JNEUROSCI.0633-20.2020. Epub 2021 Jan 21.
The acquisition of neuronal polarity is a complex molecular process that depends on changes in cytoskeletal dynamics and directed membrane traffic, regulated by the Rho and Rab families of small GTPases, respectively. However, during axon specification, a molecular link that couples these protein families has yet to be identified. In this paper, we describe a new positive feedback loop between Rab8a and Cdc42, coupled by Tuba, a Cdc42-specific guanine nucleotide-exchange factor (GEF), that ensures a single axon generation in rodent hippocampal neurons from embryos of either sex. Accordingly, Rab8a or Tuba gain-of-function generates neurons with supernumerary axons whereas Rab8a or Tuba loss-of-function abrogated axon specification, phenocopying the well-established effect of Cdc42 on neuronal polarity. Although Rab8 and Tuba do not interact physically, the activity of Rab8 is essential to generate a proximal to distal axonal gradient of Tuba in cultured neurons. Tuba-associated and Rab8a-associated polarity defects are also evidenced , since dominant negative (DN) Rab8a or Tuba knock-down impairs cortical neuronal migration in mice. Our results suggest that Tuba coordinates directed vesicular traffic and cytoskeleton dynamics during neuronal polarization. The morphologic, biochemical, and functional differences observed between axon and dendrites, require dramatic structural changes. The extension of an axon that is 1 µm in diameter and grows at rates of up to 500 µm/d, demands the confluence of two cellular processes: directed membrane traffic and fine-tuned cytoskeletal dynamics. In this study, we show that both processes are integrated in a positive feedback loop, mediated by the guanine nucleotide-exchange factor (GEF) Tuba. Tuba connects the activities of the Rab GTPase Rab8a and the Rho GTPase Cdc42, ensuring the generation of a single axon in cultured hippocampal neurons and controlling the migration of cortical neurons in the developing brain. Finally, we provide compelling evidence that Tuba is the GEF that mediates Cdc42 activation during the development of neuronal polarity.
神经元极性的获得是一个复杂的分子过程，依赖于细胞骨架动力学的变化和定向膜运输，分别由 Rho 和 Rab 家族的小 GTPase 调节。然而，在轴突特化期间，尚未确定连接这些蛋白家族的分子链接。在本文中，我们描述了 Rab8a 和 Cdc42 之间的新的正反馈回路，通过 Tuba 连接，Tuba 是 Cdc42 特异性鸟嘌呤核苷酸交换因子 (GEF)，可确保来自雄性或雌性胚胎的啮齿动物海马神经元中产生单个轴突。相应地，Rab8a 或 Tuba 的功能获得会产生具有多余轴突的神经元，而 Rab8a 或 Tuba 的功能丧失会破坏轴突特化，模拟 Cdc42 对神经元极性的既定影响。尽管 Rab8 和 Tuba 没有物理相互作用，但 Rab8 的活性对于在培养神经元中产生 Tuba 的近端到远端轴突梯度是必不可少的。Tuba 相关和 Rab8a 相关的极性缺陷也得到了证明，因为显性负性 (DN) Rab8a 或 Tuba 敲低会损害小鼠皮质神经元的迁移。我们的结果表明，Tuba 在神经元极化过程中协调定向囊泡运输和细胞骨架动力学。轴突和树突之间观察到的形态、生化和功能差异，需要剧烈的结构变化。直径为 1 µm 的轴突的延伸和高达 500 µm/d 的生长速度，需要两个细胞过程的融合：定向膜运输和精细调节的细胞骨架动力学。在这项研究中，我们表明这两个过程都整合在一个正反馈回路中，由鸟嘌呤核苷酸交换因子 (GEF) Tuba 介导。Tuba 将 Rab GTPase Rab8a 和 Rho GTPase Cdc42 的活性连接起来，确保在培养的海马神经元中产生单个轴突，并控制发育中大脑皮质神经元的迁移。最后，我们提供了令人信服的证据表明，Tuba 是介导神经元极性发育过程中 Cdc42 激活的 GEF。
