MYOSIN-BASED CORTICAL TENSION IN DICTYOSTELIUM RESOLVED INTO HEAVY AND LIGHT CHAIN-REGULATED COMPONENTS

Cortical tension in most nonmuscle cells is due largely to force produ ction by conventional myosin (myosin II) assembled into the cytoskelet on. Cytoskeletal contraction in smooth muscle and nonmuscle cells is i nfluenced by the degree of myosin filament assembly, and by activation of myosin motor function via regulatory light chain phosphorylation. Recombinant Dictyostelium discoideum cell lines have been generated be aring altered myosin heavy chains, resulting in either constitutive mo tor function or constitutive assembly into the cytoskeleton. Analysis of these cells allowed stiffening responses to agonists, measured on s ingle cells, to be resolved into an regulatory light chain-mediated co mponent reflecting activation of motor function, and a myosin heavy ch ain phosphorylation-regulated component reflecting assembly of filamen ts into the cytoskeleton. These two components can account for all of the cortical stiffening response seen during tested in vivo contractil e events.