Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637, USA.
Mol Biol Cell. 2011 Apr 15;22(8):1330-9. doi: 10.1091/mbc.E10-11-0891. Epub 2011 Feb 9.
The regulation of cellular traction forces on the extracellular matrix is critical to cell adhesion, migration, proliferation, and differentiation. Diverse lamellar actin organizations ranging from contractile lamellar networks to stress fibers are observed in adherent cells. Although lamellar organization is thought to reflect the extent of cellular force generation, understanding of the physical behaviors of the lamellar actin cytoskeleton is lacking. To elucidate these properties, we visualized the actomyosin dynamics and organization in U2OS cells over a broad range of forces. At low forces, contractile lamellar networks predominate and force generation is strongly correlated to actomyosin retrograde flow dynamics with nominal change in organization. Lamellar networks build ∼60% of cellular tension over rapid time scales. At high forces, reorganization of the lamellar network into stress fibers results in moderate changes in cellular tension over slower time scales. As stress fibers build and tension increases, myosin band spacing decreases and α-actinin bands form. On soft matrices, force generation by lamellar networks is unaffected, whereas tension-dependent stress fiber assembly is abrogated. These data elucidate the dynamic and structural signatures of the actomyosin cytoskeleton at different levels of tension and set a foundation for quantitative models of cell and tissue mechanics.
细胞对细胞外基质的牵引力的调节对细胞黏附、迁移、增殖和分化至关重要。在黏附细胞中，可以观察到从收缩片状网络到应力纤维的各种片状肌动蛋白组织。尽管片状组织被认为反映了细胞力产生的程度，但对片状肌动蛋白细胞骨架的物理行为的理解还很缺乏。为了阐明这些特性，我们在广泛的力范围内可视化了 U2OS 细胞中的肌动球蛋白动力学和组织。在低力下，收缩片状网络占主导地位，力的产生与肌球蛋白逆行流动动力学密切相关，组织形态学几乎没有变化。片状网络在快速时间尺度上产生约 60%的细胞张力。在高力下，片状网络重新组织成应力纤维，导致细胞张力在较慢的时间尺度上发生适度变化。随着应力纤维的构建和张力的增加，肌球蛋白带间距减小，α-辅肌动蛋白带形成。在软基质上，片状网络产生的力不受影响，而依赖于张力的应力纤维组装则被阻断。这些数据阐明了不同张力水平下肌动球蛋白细胞骨架的动态和结构特征，并为细胞和组织力学的定量模型奠定了基础。
