Redundant mechanisms for anaphase chromosome movements: crane-fly spermatocyte spindles normally use actin filaments but also can function without them |
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Authors: | Lacramioara Fabian Arthur Forer |
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Institution: | (1) Biology Department, York University, Toronto, Ontario |
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Abstract: | Summary. Actin inhibitors block or slow anaphase chromosome movements in crane-fly spermatocytes, but stopping of movement is only
temporary; we assumed that cells adapt to loss of actin by switching to mechanism(s) involving only microtubules. To test
this, we produced actin-filament-free spindles: we added latrunculin B during prometaphase, 9–80 min before anaphase, after
which chromosomes generally moved normally during anaphase. We confirmed the absence of actin filaments by staining with fluorescent
phalloidin and by showing that cytochalasin D had no effect on chromosome movement. Thus, actin filaments are involved in
normal anaphase movements, but in vivo, spindles nonetheless can function normally without them. We tested whether chromosome
movements in actin-filament-free spindles arise via microtubules by challenging such spindles with anti-myosin drugs. Y-27632
and BDM (2,3-butanedione monoxime), inhibitors that affect myosin at different regulatory levels, blocked chromosome movement
in normal spindles and in actin-filament-free spindles. We tested whether BDM has side effects on microtubule motors. BDM
had no effect on ciliary and sperm motility or on ATPase activity of isolated ciliary axonemes, and thus it does not directly
block dynein. Nor does it block kinesin, assayed by a microtubule sliding assay. BDM could conceivably indirectly affect these
microtubule motors, though it is unlikely that it would have the same side effect on the motors as Y-27632. Since BDM and
Y-27632 both affect chromosome movement in the same way, it would seem that both affect spindle myosin; this suggests that
spindle myosin interacts with kinetochore microtubules, either directly or via an intermediate component.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s00709-005-0094-6
Correspondence and reprints: Biology Department, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada. |
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Keywords: | : Chromosome movement Myosin Microtubule 2 3-Butanedione monoxime Latrunculin B Crane-fly spermatocyte Rho-kinase inhibitor Y-27632 |
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