Analysis of a Novel Protein Shootin1, which is involved in organization of an asymmetric signal for neuronal polarization

神经元的基本功能是接收、整合和传递信号。为了做到这一点，大多数神经元通过形成单个轴突和多个树突来形成极性。即使在对称的体外环境中，神经元也具有显著的极化能力。虽然最近的研究表明，不对称的细胞内信号可以诱导神经元极化，但在没有不对称提示的情况下，这些极化信号是如何组织的还不清楚。我们最近描述了一种细胞内蛋白Shootin1，它在神经元极化中发挥关键作用。在对称性破坏阶段，Shootin1表达上调，在轴突顶端的生长锥中经历波动积累，最终不对称地积累在单个生长锥中。神经生长锥中Shootin1的积累也促进了轴突的伸长。在这项研究中，我们研究了Shootin1诱导神经突起生长的分子机制以及Shootin1不对称信号的产生机制。Shootin1不仅作为PI3-Kinase的上游调节因子，还通过将细胞黏附分子L1-CAM作为“离合器分子”连接到肌动蛋白细丝的逆流上，从而促进轴突的延长。我们还获得的数据表明，在神经元极化过程中，生长锥体中Shootin1信号的正反馈放大有助于产生不对称的Shootin 1信号。我们还成功地产生了Shootin 1基因敲除小鼠，目前正在分析它们的表型。

The basic function of neurons is to receive, integrate and transmit signals. To do so, most neurons develop polarity by forming a single axon and multiple dendrites. Neurons have the remarkable ability to polarize even in symmetrical in vitro environments. Although recent studies have shown that asymmetric intracellular signals can induce neuronal polarization, it remains unclear how these polarized signals are organized without asymmetric cues. We recently described an intracellular protein, shootin1, which plays a critical role in neuronal polarization. During the symmetry breaking step, shootin1 becomes up-regulated, undergoes a fluctuating accumulation in growth cones at neurite tips, and eventually accumulates asymmetrically in a single growth cone. Accumulation of shootin1 in nerve growth cones also enhanced neurite elongation. In this study, we examined molecular mechanisms for shootin1-induced neurite outgrowth and the mechanisms for generation of asymmetric signal of shootin1. Shootin1 not only acted as a upstream regulator of PI 3-kinase but also enhanced neurite elongation, by linking a cell adhesion molecule Ll-CAM to actin filament retrograde flow as a "clutch molecule". We also obtained data to suggest that positive feedback amplification of shootin1 signal in growth cones contributes to generation of asymmetric shootin 1 signals during neuronal polarization. We also succeeded in generation of shootin 1 knockout mice, and are currently analyzing their phenotypes.