Laboratoire de Physiologie Cellulaire Végétale, Institut de Recherches en Technologies et Sciences pour le Vivant, CNRS/CEA/INRA/UJF, 38054 Grenoble, France.
Curr Biol. 2010 Mar 9;20(5):423-8. doi: 10.1016/j.cub.2009.12.056. Epub 2010 Feb 25.
Cells use actin assembly to generate forces for membrane protrusions during movement [1] or, in the case of pathogens, to propel themselves in the host cells, in crude extracts [2], or in mixtures of actin and other purified proteins [3]. Significant progress has been made in understanding the mechanism of actin-based motility at a macroscopic level by using biomimetic systems in vitro [4-6]. Here, we combined such a system with evanescent wave microscopy to visualize Arp2/3-mediated actin network formation at single-actin-filament resolution. We found that actin filaments that we call "primers" determine the origin of the autocatalytic and propagative formation of the actin network. In the presence of capping protein, multiple "primers" generate independent networks that merge around the object to form an outer "shell" made of entangled and capped filaments. Simultaneously, newly created filaments on the surface of the particle initiate mechanical stress, which develops until symmetry breaking. Our results and extensive modeling support that the stress, which releases into propulsive forces [7], is controlled not by any specific orientation of actin filaments toward the nucleation sites but only by new monomers added near the load surface.
细胞利用肌动蛋白组装来产生运动过程中膜突起的力[1]，或者在病原体的情况下，在宿主细胞中推动自身前进，在粗提物[2]中，或在肌动蛋白和其他纯化蛋白的混合物[3]中。通过使用体外仿生系统，在宏观水平上理解基于肌动蛋白的运动机制已经取得了重大进展[4-6]。在这里，我们将这种系统与消逝波显微镜结合使用，以单肌动蛋白丝分辨率可视化 Arp2/3 介导的肌动蛋白网络形成。我们发现，我们称之为“引物”的肌动蛋白丝决定了肌动蛋白网络的自催化和传播形成的起源。在盖帽蛋白存在的情况下，多个“引物”生成独立的网络，在物体周围合并形成由缠结和盖帽的纤维制成的外部“壳”。同时，颗粒表面上新生成的纤维会引发机械应力，直到对称性破坏为止。我们的结果和广泛的建模支持这样一种观点，即释放到推进力中的应力[7]不是由肌动蛋白纤维朝向成核位点的任何特定取向控制的，而是仅由负载表面附近添加的新单体控制的。
