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Published 24 April 2006. doi:10.1083/jcb.200601075
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 173, Number 2, 173-179
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Kinesin 5–independent poleward flux of kinetochore microtubules in PtK1 cells



Lisa A. Cameron1, Ge Yang2, Daniela Cimini1, Julie C. Canman1, Olga Kisurina-Evgenieva3, Alexey Khodjakov3,4, Gaudenz Danuser2, and E.D. Salmon1

1 Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
2 Laboratory for Computational Cell Biology, Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037
3 Wadsworth Center, New York State Department of Health, Albany, NY 12201
4 Department of Biomedical Sciences, State University of New York at Albany, Albany, NY 12222

Correspondence to Lisa Cameron: lcameron{at}email.unc.edu; or E.D. Salmon: tsalmon{at}email.unc.edu

Forces in the spindle that align and segregate chromosomes produce a steady poleward flux of kinetochore microtubules (MTs [kMTs]) in higher eukaryotes. In several nonmammalian systems, flux is driven by the tetrameric kinesin Eg5 (kinesin 5), which slides antiparallel MTs toward their minus ends. However, we find that the inhibition of kinesin 5 in mammalian cultured cells (PtK1) results in only minor reduction in the rate of kMT flux from ~0.7 to ~0.5 µm/min, the same rate measured in monopolar spindles that lack antiparallel MTs. These data reveal that the majority of poleward flux of kMTs in these cells is not driven by Eg5. Instead, we favor a polar "pulling-in" mechanism in which a depolymerase localized at kinetochore fiber minus ends makes a major contribution to poleward flux. One candidate, Kif2a (kinesin 13), was detected at minus ends of fluxing kinetochore fibers. Kif2a remains associated with the ends of K fibers upon disruption of the spindle by dynein/dynactin inhibition, and these K fibers flux.

J.C. Canman's present address is Institute of Molecular Biology, University of Oregon, Eugene, OR 97402.

Abbreviations used in this paper: FSM, fluorescent speckle microscopy; kMT, kinetochore MT; MT, microtubule; PA, photoactivatable; qFSM, quantitative FSM.


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