Functions of Cytoplasmic Fibers in Non-Muscle Cell Motility

The finding of several types of fibers in the cytoplasm of a wide variety of cells has led to an increased interest in the general problem of non-muscle cell motility. The most extensively studied of these cytoplasmic fibers is the microtubule, which is thought to be directly involved in such diverse aspects of motility as chromosome movements during mitosis (Inoué and Sato, 1967), intracellular transport of organelles (Bickle et al., 1965; Freed and Lebowitz, 1970), and in the movement of cells during morphogenesis (Tilney and Gibbins, 1969; Byers and Porter, 1964). Microtubules are also considered to be the major component of a cytoskeletal system involved in the formation and maintenance of asymmetric cellular processes (Tilney and Gibbins, 1969; Tilney and Porter, 1965, 1967; Tilney et al., 1966; Goldman, 1971). Microfilaments, a second type of cytoplasmic fiber, are thought to function in cytoplasmic streaming, cytokinesis, membrane ruffling, cell locomotion, endocytosis and...