Two mitotic kinesins cooperate to drive sister chromatid separation during anaphase

Abstract

During anaphase identical sister chromatids separate and move towards opposite poles of the mitotic spindle. In the spindle, kinetochore microtubules have their plus ends embedded in the kinetochore and their minus ends at the spindle pole. Two models have been proposed to account for the movement of chromatids during anaphase. In the 'Pac-Man' model, kinetochores induce the depolymerization of kinetochore microtubules at their plus ends, which allows chromatids to move towards the pole by 'chewing up' microtubule tracks. In the 'poleward flux' model, kinetochores anchor kinetochore microtubules and chromatids are pulled towards the poles through the depolymerization of kinetochore microtubules at the minus ends. Here, we show that two functionally distinct microtubule-destabilizing KinI kinesin enzymes (so named because they possess a kinesin-like ATPase domain positioned internally within the polypeptide) are responsible for normal chromatid-to-pole motion in Drosophila. One of them, KLP59C, is required to depolymerize kinetochore microtubules at their kinetochore-associated plus ends, thereby contributing to chromatid motility through a Pac-Man-based mechanism. The other, KLP10A, is required to depolymerize microtubules at their pole-associated minus ends, thereby moving chromatids by means of poleward flux.

The perpetual movements of anaphase

“…Taken together, these results suggest that microtubule depolymerization at the poles acts as a governor that limits and regulates spindle length in response to external force producers that slide microtubules poleward [65], similar to what has been proposed for spindle elongation during anaphase B [67]. According to this model, one would predict that inhibition of Klp10A or Kif2a attenuates "flux" even if the force sliding microtubules poleward is still present, consistent with what has been experimentally observed [61,64,65,70].…”

“…The microtubule depolymerizing activity at the poles has been attributed to the kinesin-13 protein Kif2a in Xenopus and mammals, and to Klp10A in Drosophila [51,61,62,69,70]. However, the fact that newly created kinetochore microtubule minusends by laser microsurgery are stable but are still able to slide poleward at flux rates in metaphase [52,65] suggests that the microtubule depolymerizing activity at the poles might be a cellular response to regulate spindle length, and not necessarily the fluxdriving force.…”

Prime movers: the mechanochemistry of mitotic kinesins

“…1d, insets 10 and 11). Experiments in D. melanogaster show that Kinesin-13-driven microtubule depolymerization (see above and BOX 2) is crucial for a combined "Pacman-flux" mechanism 147 . It is suggested that the end-tracking properties of kinesin-7 and kinesin-8 family members (KIF10 and KIF18A, respectively) may assist kinetochores in maintaining attachment to depolymerizing microtubules 148 .…”

Drosophila S2 Cells as a Model System to Investigate Mitotic Spindle Dynamics, Architecture, and Function

“…When we use RNAi to knockdown KLP10A, a kinesin 13 protein, microtubules elongate due to the reduction of depolymerization activity at the poles (Fig. 3E) (Rogers et al, 2004). Conversely, when CLASP is perturbed, new tubulin molecules are not incorporated at kinetochore microtubules, while microtubule depolymerization still occurs at the poles (Maiato et al, 2005).…”

“…However, microtubules, including those attached at kinetochores, remain dynamic and can be recycled due to turnover (Gorbsky and Borisy, 1989;Zhai et al, 1995) and poleward flux (Mitchison, 1989). This requires a labile interface that enables microtubules to slip and eventually detach from the kinetochore in response to a poleward force, whose origin remains controversial (Cameron et al, 2006;Dumont and Mitchison, 2009;Ganem et al, 2005;Matos et al, 2009;Miyamoto et al, 2004;Rogers et al, 2004). The importance of a labile kinetochore-microtubule interface is reflected in the capacity to correct mistakes inherent to the stochastic nature of mitotic spindle assembly and the interaction between microtubules and chromosomes (Bakhoum et al, 2009b;Ganem et al, 2005;Matos et al, 2009).…”