Possible roles of actin and myosin during anaphase chromosome movements in locust spermatocytes

We tested whether the mechanisms of chromosome movement during anaphase in locust [Locusta migratoria (L.)] spermatocytes might be similar to those described in crane-fly spermatocytes. Actin and myosin have been implicated in anaphase chromosome movements in crane-fly spermatocytes as indicated by effects of inhibitors and by localisations of actin and myosin in spindles. In this study we tested whether locust spermatocytes spindles also utilize actin and myosin and whether actin is involved in microtubule flux. Living locust spermatocytes were treated with inhibitors of actin (Latrunculin B and Cytochalasin D), an inhibitor of myosin (BDM), or inhibitors of myosin phosphorylation (Y-27632 and ML-7). We added drugs (individually) during anaphase. Actin inhibitors alter anaphase: chromosomes either completely stop moving, slow, or sometimes accelerate. The myosin inhibitor, BDM, also alters anaphase: in most cases, the chromosomes drastically slow or stop. ML-7, an inhibitor of MLCK, causes chromosomes to stop, slow, or sometimes accelerate, similar to actin inhibitors. Y27632, an inhibitor of Rho-kinase, drastically slows or stops anaphase chromosome movements. The effects of the drugs on anaphase movement are reversible: most of the half-bivalents resume movement at normal speed after these drugs are washed out. Actin and myosin were present in the spindles in locations consistent with their possible involvement in force production. Microtubule flux along kinetochore fibres is an actin-dependent process, since LatB removes completely or drastically reduces the gap in microtubule acetylation at the kinetochore. These results suggest that actin and myosin are involved in anaphase chromosome movements in locust spermatocytes.