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© The Rockefeller University Press, 0021-9525/1999//1019 $5.00
The Journal of Cell Biology, Volume 146, Number 5, , 1999 1019-1032

Original Article

The Role of Actin in Spindle Orientation Changes during the Saccharomyces cerevisiae Cell Cycle



Chandra L. Theesfelda, Javier E. Irazoquia, Kerry Bloomb, and Daniel J. Lewa

a Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710
b Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710.(919) 681-1005(919) 613-8627

daniel.lew{at}duke.edu

In the budding yeast Saccharomyces cerevisiae, the mitotic spindle must align along the mother-bud axis to accurately partition the sister chromatids into daughter cells. Previous studies showed that spindle orientation required both astral microtubules and the actin cytoskeleton. We now report that maintenance of correct spindle orientation does not depend on F-actin during G2/M phase of the cell cycle. Depolymerization of F-actin using Latrunculin-A did not perturb spindle orientation after this stage. Even an early step in spindle orientation, the migration of the spindle pole body (SPB), became actin-independent if it was delayed until late in the cell cycle.

Early in the cell cycle, both SPB migration and spindle orientation were very sensitive to perturbation of F-actin. Selective disruption of actin cables using a conditional tropomyosin double-mutant also led to de- fects in spindle orientation, even though cortical actin patches were still polarized. This suggests that actin cables are important for either guiding astral microtubules into the bud or anchoring them in the bud. In addition, F-actin was required early in the cell cycle for the development of the actin-independent spindle orientation capability later in the cell cycle. Finally, neither SPB migration nor the switch from actin-dependent to actin-independent spindle behavior required B-type cyclins.

Key Words: actin • spindle • cell cycle • astral microtubule • Latrunculin-A

© 1999 The Rockefeller University Press

1.used in this paper: DAPI, 4',6-diamidino-2-phenylindole; DIC, differential interference contrast; Lat-A, Latrunculin-A; SPB, spindle pole body

Chandra L. Theesfeld and Javier E. Irazoqui contributed equally to this work.


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Related Article

In Brief
J. Cell Biol. 1999 146: 1-2. [Full Text] [PDF]





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