Laboratory for Developmental Neurobiology, Brain Science Institute, The Institute of Physical and Chemical Research, Wako, Saitama 351-0198, Japan.
J Neurosci. 2011 May 18;31(20):7357-64. doi: 10.1523/JNEUROSCI.2718-10.2011.
Growth cone collapse is a crucial process for repulsive axon guidance and is accompanied by a reduction in growth cone surface area. This process of reduction may be regulated by endocytosis; however, its molecular mechanism is unclear. Macropinocytosis is a clathrin-independent form of endocytosis in which large areas of plasma membrane can be engulfed. We have reported previously that macropinocytosis is induced in growth cones of chick dorsal root ganglion neurons by semaphorin 3A (Sema3A), a repulsive axon guidance cue, and that Sema3A-induced reduction in growth cone surface area and macropinocytic vacuole area were correlated, suggesting a positive role for macropinocytosis in Sema3A-induced growth cone collapse. In the present study, we found that syntaxin 1B (Syx1B), a membrane trafficking protein, is a negative regulator of macropinocytosis, and its expression is downregulated by Sema3A signaling. Macropinocytosis inhibitor ethylisopropylamiloride or Syx1B overexpression suppressed Sema3A-induced macropinocytosis and growth cone collapse. These results indicate that Syx1B couples macropinocytosis-mediated massive internalization of the plasma membrane to Sema3A-induced growth cone collapse.
生长锥塌陷是排斥性轴突导向的一个关键过程，伴随着生长锥表面积的减少。这个减少过程可能受到胞吞作用的调节；然而，其分子机制尚不清楚。巨胞饮作用是网格蛋白非依赖性的胞吞作用形式，其中大量的质膜可以被吞噬。我们之前曾报道过，排斥性轴突导向信号分子 semaphorin 3A（Sema3A）可诱导鸡背根神经节神经元生长锥中的巨胞饮作用，并且 Sema3A 诱导的生长锥表面积和巨胞饮空泡面积的减少呈正相关，这表明巨胞饮作用在 Sema3A 诱导的生长锥塌陷中起积极作用。在本研究中，我们发现膜转运蛋白 syntaxin 1B（Syx1B）是巨胞饮作用的负调控因子，其表达受 Sema3A 信号的下调。巨胞饮作用抑制剂乙基异丙基amiloride 或 Syx1B 的过表达抑制了 Sema3A 诱导的巨胞饮作用和生长锥塌陷。这些结果表明，Syx1B 将质膜的巨胞饮作用介导的大量内化与 Sema3A 诱导的生长锥塌陷偶联。
