Nonmuscle Actin and Myosin

Actin and myosin appear to play major roles in cell motility and changes of cell shape.

Actin is a major component of the cytoskeleton-the fibrous array that pervades almost every kind of cell and gives it a specific shape.

Nonmuscle myosin is different in sequence from muscle myosin. Rather than forming thick filaments, nonmuscle myosin tends to form dimers, interacting with cytoplasmic actin to form a loose contractile network. Organized contraction and relaxation of such networks lead to a wide variety of cell movements and responses, including amoeboid crawling.

Actin-myosin contractile complexes are also involved in cytokinesis - the division of cells in the last stages of mitosis (Figure 8.17). Myosin is essential for cytokinesis, but is not essential for the contractile process in the mitotic spindle.

See also: Microtubule Systems, Actin and Myosin