Deformations Within Moving Kinetochores Reveal Different Sites of Active and Passive Force Generation

Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA.
Science (Impact Factor: 33.61). 06/2012; 337(6092):355-8. DOI: 10.1126/science.1221886
Source: PubMed


Kinetochores mediate chromosome segregation at mitosis. They are thought to contain both active, force-producing and passive,
frictional interfaces with microtubules whose relative locations have been unclear. We inferred mechanical deformation within
single kinetochores during metaphase oscillations by measuring average separations between fluorescently labeled kinetochore
subunits in living cells undergoing mitosis. Inter-subunit distances were shorter in kinetochores moving toward poles than
in those moving away. Inter-subunit separation decreased abruptly when kinetochores switched to poleward movement and decreased
further when pulling force increased, suggesting that active force generation during poleward movement compresses kinetochores.
The data revealed an active force-generating interface within kinetochores and a separate passive frictional interface located
at least 20 nanometers away poleward. Together, these interfaces allow persistent attachment with intermittent active force

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    • "Both the model and the experimental data also show that the AP-moving KT reaches its maximum speed earlier than the P-moving KT (Fig. 5, I and J; and Fig. 1, E and F, insets; Wan et al., 2012). In fact, these differences in acquisition of the maximal speed during P and AP movement are responsible for the observed period doubling in the inter-KT distance (Dumont et al., 2012; Wan et al., 2012; Fig. 5 A). Our model suggests that this is due to the biphasic kinetics of the Ndc80 bonds attached to depolymerizing MTs, resulting in a slower turnover of the kMT bonds of the P-moving sister (under moderate tension), hindering the increase in P velocity until a critical tension level is reached. "
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    • "The observed structural changes at kinetochores have been assumed to correlate with the presence of tension, but thus far, such studies have not made direct measurements of force or tension. Nevertheless, careful quantitative analysis of the dynamic changes in the distances between CENP-C and Hec1 or Cdc20 during sister chromatid oscillations has supported the model that changes in intrakinetochore distance are force dependent (Dumont et al., 2012). However, these structural alterations may also be the result of changes in the conformation, organization, or localization of proteins within the kinetochore. "
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