Actin in sperm tails and meiotic spindles.

Abstract

IN many cases cellular motility seems to be due to interactions between actin and myosin1–8. Actin (or actin-like material) has also been identified in other cellular systems which exhibit motility9–14 and actin-like and myosin-like proteins have been claimed to be isolated from mitochondria15 and chloroplasts16. While it is not proved that motility in these systems is due to actin and myosin, actin-myosin interactions are probably involved. Flagellar (ciliary) motions and chromosome movements, on the other hand, have generally been attributed to microtubules17–19, and thus there seemed to be two different kinds of motile systems; one based on actin-myosin interactions and the other on microtubules. We have found, however, actin-like filaments in both sperm tails (flagellae) and meiotic spindles of crane flies. Although we are well aware that we have demonstrated merely the presence of actin and have by no means proven that the flagellar and spindle actin has anything to do with motility, we nonetheless suggest that motility in all motile systems in higher cells is based on actin-myosin interactions.