Separate but not equal: Differential mechanical roles for myosin isoforms

Cells undergo many structural-mechanical changes as an inextricable component of cellular motility, cytokinesis, and changes in cell shape. The mere act of receptor-mediated adhesion to extracellular matrix involves massive changes in cytoskeletal organization, spreading, and flattening of cells against the matrix, and the generation of traction forces through the contractile activity of cells. The primary force-generating proteins involved in these mechanical processes are thought to be the nonmuscle myosin II's (NMM-II). Of the three different nonmuscle myosin II isoforms that have been identified, two (NMM-IIA and NMM-IIB) are found almost ubiquitously in higher organisms. Yet, it has remained unclear whether these molecules play redundant, overlapping, or distinct roles in the varying mechanical functions of cells.