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Browsing Faculty of Science by Subject "actin"
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Item Open Access Jasplakinolide, an actin stabilizing agent, alters anaphase chromosome movements in crane‐fly spermatocytes(Wiley, 2008-11) Forer, Arthur; Xie, LeleWe added jasplakinolide to anaphase crane-fly spermatocytes and determined its effects on chromosome movement. Previous work showed that actin depolymerizing agents such ascytochalasin D or latrunculin B blocked or slowed chromosome movements; we wanted to compare the effects of jasplakinolide, a compound that stabilizes actin filaments against depolymerization. Jasplakinolide had the same effect on movements of each half-bivalent in a separating pair of half-bivalents, but different half-bivalent pairs in the same cell often responded differently, even when the concentrations of jasplakinolide varied by a factor of two. Jasplakinolide had no effect on about20% of the pairs, but otherwise caused movements to slow, or to stop, or, rarely, to accelerate. When cells were kept in jasplakinolide, stopped pairs eventually resumed movement; slowed pairs did not change their speeds. Confocal microscopy indicated that neither the distributions of spindle actin filaments nor the distributions of spindle microtubules were altered by the jasplakinolide. It is possible that jasplakinolide binds to spindle actin and blocks critical binding sites, but we suggest that jasplakinolide affects anaphase chromosome movement by preventing actin-filament depolymerization that is necessary for anaphase to proceed. Overall, our data indicate that actin is involved in one of the redundant mechanisms cells use to move chromosomes.Item Open Access Possible roles of actin and myosin during anaphase chromosome movements in locust spermatocytes(Springer Link, 2007-10) Forer, Arthur; Fabian, LacramioaraWe 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.Item Open Access What generates flux of tubulin in kinetochore microtubules?(Springer Link, 2008-04) Forer, Arthur; Pickett-Heaps, Jeremy; Spurck, TimWe discuss models for production of tubulin flux in kinetochore microtubules. Current models concentrate solely on microtubules and their associated motors and enzymes. For example, in some models the driving force for flux is enzymes at the poles and the kinetochores; in others the driving force is motor molecules that are associated with a stationary spindle matrix. We present a different viewpoint, that microtubules are propelled poleward by forces arising from the spindle matrix, that the forces on the microtubules "activate" polymerising and depolymerising enzymes at kinetochores and poles, that matrix forces utilise actin, myosin, and microtubule motors, and that the matrix itself may not necessarily be static.