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J Cell Biol 2003 Aug 04;1623:377-82. doi: 10.1083/jcb.200301088.
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Direct observation of microtubule dynamics at kinetochores in Xenopus extract spindles: implications for spindle mechanics.

Maddox P , Straight A , Coughlin P , Mitchison TJ , Salmon ED .

Microtubule plus ends dynamically attach to kinetochores on mitotic chromosomes. We directly imaged this dynamic interface using high resolution fluorescent speckle microscopy and direct labeling of kinetochores in Xenopus extract spindles. During metaphase, kinetochores were stationary and under tension while plus end polymerization and poleward microtubule flux (flux) occurred at velocities varying from 1.5-2.5 micro m/min. Because kinetochore microtubules polymerize at metaphase kinetochores, the primary source of kinetochore tension must be the spindle forces that produce flux and not a kinetochore-based mechanism. We infer that the kinetochore resists translocation of kinetochore microtubules through their attachment sites, and that the polymerization state of the kinetochore acts a "slip-clutch" mechanism that prevents detachment at high tension. At anaphase onset, kinetochores switched to depolymerization of microtubule plus ends, resulting in chromosome-to-pole rates transiently greater than flux. Kinetochores switched from persistent depolymerization to persistent polymerization and back again during anaphase, bistability exhibited by kinetochores in vertebrate tissue cells. These results provide the most complete description of spindle microtubule poleward flux to date, with important implications for the microtubule-kinetochore interface and for how flux regulates kinetochore function.

PubMed ID: 12900391
PMC ID: PMC2172681
Article link: J Cell Biol
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: abl1 camkmt cenpa cenpe dnai1 dync1li1 kidins220 tbxt.2
Antibodies: Cenpa Ab1

Article Images: [+] show captions
References [+] :
Brust-Mascher, Microtubule flux and sliding in mitotic spindles of Drosophila embryos. 2002, Pubmed