Spatially Dissecting the Viscoelastic Recoil and Cell Shape Contributions of Actomyosin Stress Fiber Bundles

Abstract

The ability of a living cell to distribute contractile stresses against the extracellular matrix (ECM) in a spatially heterogeneous fashion underlies many fundamental behaviors, including motility, polarity, and assembly into multicellular tissues. Here we investigate the biophysical basis of this phenomenon at unprecedented spatial and mechanical resolution by using femtosecond laser ablation to sever contractile stress fibers located in specific cellular compartments and measure regional variations in fiber viscoelastic retraction and contribution to cell shape stability. Upon photodisruption, myosin light chain kinase-dependent stress fibers located along the cell periphery recoil much more slowly than rho-associated kinase-dependent stress fibers located in the cell center, with severing of peripheral fibers uniquely triggering a dramatic contraction of the entire cell. Remarkably, selective pharmacological dissipation of peripheral fibers significantly accelerates the retraction of central fibers, suggesting transference of tensile loads from one population of stress fibers to another in order to stabilize cell shape. These results suggest that stress fibers regulated by different myosin activators exhibit different mechanical properties and cell shape contributions. These data also illustrate the potential of femtosecond laser ablation to spatially map the microscale contractile mechanics of living cells.