Tension-dependent formation of stress' fibers in fibroblasts: A study using semi-intact cells

Stress fiber is a bundle of actin filaments, which also contains myosin and cross-linking proteins. It remains unclear how stress fibers are formed from their main components, actin and myosin. To address this question we examined the process of formation of stress fibers in a model system, a semi-intact cell. Fibroblasts were treated with a Rho kinase inhibitor to disorganize stress fibers. These cells were permeabilized and used as semi-intact cells in this study. When these cells were treated with ATP and Ca2+, stress fibers were restored within 15 min. Motion analysis of actin filaments labeled with quantum dots during formation of stress fibers revealed actin filaments were gradually assembled while they were moving toward the center of the cell. This suggests that ATP-driven tension influences the stress fiber formation. The ATP-driven tension was mimicked in this study by artificial centripetal traction force, which was carried out by dragging the micropipette attached on the cell surface. Stress fibers were formed by the traction force application. These results suggest that tension in actomyosin meshwork is an important element in stress fiber formation.