Koestler Stefan A, Auinger Sonja, Vinzenz Marlene, Rottner Klemens, Small J Victor
Institute of Molecular Biotechnology, Austrian Academy of Sciences, Dr. Bohr-Gasse 3, 1030, Vienna, Austria.
Nat Cell Biol. 2008 Mar;10(3):306-13. doi: 10.1038/ncb1692. Epub 2008 Feb 17.
Eukaryotic cells advance in phases of protrusion, pause and withdrawal. Protrusion occurs in lamellipodia, which are composed of diagonal networks of actin filaments, and withdrawal terminates with the formation of actin bundles parallel to the cell edge. Using correlated live-cell imaging and electron microscopy, we have shown that actin filaments in protruding lamellipodia subtend angles from 15-90 degrees to the front, and that transitions from protrusion to pause are associated with a proportional increase in filaments oriented more parallel to the cell edge. Microspike bundles of actin filaments also showed a wide angular distribution and correspondingly variable bilateral polymerization rates along the cell front. We propose that the angular shift of filaments in lamellipodia serves in adapting to slower protrusion rates while maintaining the filament densities required for structural support; further, we suggest that single filaments and microspike bundles contribute to the construction of the lamella behind and to the formation of the cell edge when protrusion ceases. Our findings provide an explanation for the variable turnover dynamics of actin filaments in lamellipodia observed by fluorescence speckle microscopy and are inconsistent with a current model of lamellipodia structure that features actin filaments branching at 70 degrees in a dendritic array.
真核细胞经历突出、暂停和缩回阶段。突出发生在片状伪足中，片状伪足由肌动蛋白丝的对角网络组成，而缩回以平行于细胞边缘的肌动蛋白束的形成为终点。通过相关的活细胞成像和电子显微镜，我们已经表明，突出的片状伪足中的肌动蛋白丝向前的夹角为15 - 90度，并且从突出到暂停的转变与更平行于细胞边缘取向的丝的比例增加相关。肌动蛋白丝的微刺束也显示出广泛的角度分布，并相应地沿细胞前沿具有可变的双侧聚合速率。我们提出，片状伪足中丝的角度变化有助于在维持结构支撑所需的丝密度的同时适应较慢的突出速率；此外，我们认为单丝和微刺束在突出停止时有助于后面薄片的构建和细胞边缘的形成。我们的发现为荧光斑点显微镜观察到的片状伪足中肌动蛋白丝的可变周转动力学提供了解释，并且与当前的片状伪足结构模型不一致，该模型的特征是肌动蛋白丝以树状阵列在70度处分支。
