Persistent, directional motility of cells and cytoplasmic fragments in the absence of microtubules

Directional cell locomotion is displayed by many cell types both in vivo and in vitro1. In many instances, persistency and directionality are imposed by external stimuli such as chemical attractants or substrate properties2–6. Some cell types, such as fibroblasts or leukocytes, are capable of migrating in the absence of known stimuli in a pattern known as persistent random walk7, where the direction of movement is maintained for at least one cell diameter before the cell performs a sudden directional change. In many examples of persistent motility, microtubules are believed to have a key role as elements that stabilize or even determine a cell's direction of movement8–11. If disassembled, persistency is reduced or impaired12–15. Despite some reports to the contrary16–18, these and other observations have led to the widely accepted view that microtubules may be the overall organizers of cell geometry, polarity and motile activity19. Here we report that rapid, directional locomotion of fish epidermal keratocytes is independent of the presence of microtubules. Moreover, small cytoplasmic fragments derived from the anterior lamella of these cells are capable of locomoting in a pattern indistinguishable from that of intact cells. Since these fragments contain no nucleus, microtubules or centrioles, the persistency-determining component must be sought in some other component(s) of the cytoplasm, possibly the motile machinery of the lamella itself.