Michelot Alphée, Derivery Emmanuel, Paterski-Boujemaa Rajaa, Guérin Christophe, Huang Shanjin, Parcy François, Staiger Christopher J, Blanchoin Laurent
Departement Réponse et Dynamique Cellulaire, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Joseph Fourier, F38054 Grenoble, France.
Curr Biol. 2006 Oct 10;16(19):1924-30. doi: 10.1016/j.cub.2006.07.054.
Actin-filament bundles (or cables) have a structural role during cell division and morphogenesis, but also serve as important "tracks" for the transport of materials during cytokinesis and polarized cell growth. However, the dynamic formation of these longitudinal actin-filament higher-order structures is not understood. Recently, several lines of evidence suggest that formins provide one avenue for the initiation of actin cables in vivo. A popular model for the mechanism of polymerization of actin filaments by formin involves the processive movement of formin attached at the barbed end of an elongating filament. In the present study, we use an in vitro system to reconstitute the dynamic formation of actin-filament bundles generated by Arabidopsis FORMIN1 (AFH1). To be able to visualize individual events in such a complex system, we used real-time evanescent-wave microscopy. Surprisingly, we find that AFH1 is a nonprocessive formin that moves from the barbed end to the side of an actin filament after the nucleation event. We show why this new mechanism of nucleation by a member of the formin family is important for bundle formation. Finally, we analyze the different parameters controlling the dynamic formation of such longitudinal actin-filament bundles.
肌动蛋白丝束（或束状结构）在细胞分裂和形态发生过程中具有结构作用，同时在胞质分裂和极化细胞生长过程中也作为物质运输的重要“轨道”。然而，这些纵向肌动蛋白丝高阶结构的动态形成过程尚不清楚。最近，有几条证据表明，formin蛋白为体内肌动蛋白束的起始提供了一条途径。一种关于formin蛋白聚合肌动蛋白丝机制的流行模型涉及附着在伸长丝末端的formin蛋白的连续移动。在本研究中，我们使用体外系统来重建拟南芥formin1（AFH1）产生的肌动蛋白丝束的动态形成过程。为了能够在如此复杂的系统中可视化单个事件，我们使用了实时倏逝波显微镜。令人惊讶的是，我们发现AFH1是一种非连续移动的formin蛋白，在成核事件后从肌动蛋白丝的末端移动到侧面。我们展示了formin家族成员的这种新的成核机制对束状结构形成的重要性。最后，我们分析了控制这种纵向肌动蛋白丝束动态形成的不同参数。
