Abstract
A critical function of cells is to provide a force-bearing linkage from matrix to matrix, matrix to cells, or from cell to cell in a tissue and organ as well as a force generating structure. In fully differentiated skin cells, much of the force is borne by intermediate filaments. In dynamic tissues or isolated cells on matrix, high forces are generated by myosin II pulling on actin, either through stress fibers or through some other trans-cytoplasmic network. In epithelia, myosin II clearly plays a critical role in forming a contractile ring around wounds that provides turgor and restructuring forces. A major mystery is how a dynamic cytoskeleton can create a mechanically coherent cytoplasm. We suggest that the key lie in the continuous assembly of actin and myosin filaments in the cell periphery that has been recently found in isolated fibroblasts.