The Mechanical Interplay between Cell Shape and Actin Cytoskeleton Organization

The shape of adhering cells is determined by the interplay between contractile forces, arising from the cytoskeleton, and the resistance of the underlying substrate. Experiments with fibroblasts on elastic micro-pillar arrays show that fibroblasts possess a high degree of orientational order of the actin stress fibers. This anisotropy causes the shape of the cell edge and the distribution of adhesion forces to deviate from that of cells with an isotropic cytoskeleton, while at the same time this cellular shape influences the orientation of the actin stress fibers. We study this interplay between stress fiber alignment and cell shape and contractility. We theoretically describe the contractility of the cytoskeleton as a combination of directed forces, in the direction of stress fibers, and isotropic forces. We model the stress fiber organization as a competition between alignment within the cytoskeleton and alignment of the cytoskeleton with the cell edge. We compare our results to experimental data on fibroblast shape and actin cytoskeleton organization. Our work illustrates the strong coupling between anisotropy on the inside of the cell to anisotropy in shape and forces on the outside of the cell.