Aurora Kinase Promotes Turnover of Kinetochore Microtubules to Reduce Chromosome Segregation Errors

Abstract

Merotelic kinetochore orientation is a misattachment in which a single kinetochore binds microtubules from both spindle poles rather than just one and can produce anaphase lagging chromosomes, a major source of aneuploidy. Merotelic kinetochore orientation occurs frequently in early mitosis, does not block chromosome alignment at the metaphase plate, and is not detected by the spindle checkpoint. However, microtubules to the incorrect pole are usually significantly reduced or eliminated before anaphase. We discovered that the frequency of lagging chromosomes in anaphase is very sensitive to partial inhibition of Aurora kinase activity by ZM447439 at a dose, 3 microM, that has little effect on histone phosphorylation, metaphase chromosome alignment, and cytokinesis in PtK1 cells. Partial Aurora kinase inhibition increased the frequency of merotelic kinetochores in late metaphase, and the fraction of microtubules to the incorrect pole. Measurements of fluorescence dissipation after photoactivation showed that kinetochore-microtubule turnover in prometaphase is substantially suppressed by partial Aurora kinase inhibition. Our results support a preanaphase correction mechanism for merotelic attachments in which correct plus-end attachments are pulled away from high concentrations of Aurora B at the inner centromere, and incorrect merotelic attachments are destabilized by being pulled toward the inner centromere.

MCAK and Paclitaxel Have Differential Effects on Spindle Microtubule Organization and Dynamics

“…Previous work estimated that ϳ70% of the MTs were in nonkt-spindle MTs and 30% were in K-fibers (Mitchison and Salmon, 1992;Cimini et al, 2006). However, in our study we observed that only 20% of the recovery comes from the nonkt-spindle MTs and 80% is from the K-fibers.…”

“…Our measured t 1/2 values for the slow phase of the recovery for prometaphase cells are similar to those reported previously for the K-fibers . Our values for the fast phase, however, are faster than those reported by others (Saxton et al, 1984;Zhai et al, 1995;Cimini et al, 2006). One possibility is that our fast phase actually represents the diffusion of unincorporated GFP-tubulin subunits into the bleach zone.…”

“…The spindle MTs or nonkinetochore MTs (nonkt-MTs) represent the bulk of the MT polymer in the spindle and are highly dynamic, with a half-time for recovery (t 1/2 ) of ϳ18 s (Saxton et al, 1984;Cimini et al, 2006). The kinetochore MTs (K-fibers) are organized into bundles of MTs that mediate the attachment of the chromosomes to the spindle (Rieder, 1982;McDonald et al, 1992;McIntosh et al, 2002).…”

“…The kinetochore MTs (K-fibers) are organized into bundles of MTs that mediate the attachment of the chromosomes to the spindle (Rieder, 1982;McDonald et al, 1992;McIntosh et al, 2002). K-fibers are overall more stable, with a t 1/2 of ϳ5 min (Gorbsky et al, 1988;Zhai et al, 1995;Cimini et al, 2006), but locally they are highly dynamic as the polymerization/depolymerization cycles at their plus ends are coupled to chromosome movement (McIntosh et al, 2002). Astral MTs extend from the spindle pole toward the cell cortex and may be important in spindle positioning (Rosenblatt, 2005).…”

“…Our data support the model that MCAK perturbs spindle organization by acting preferentially on astral MTs and that it contributes to error correction by controlling MT dynamics in the K-fiber. Previous studies measured the dynamics of spindle MTs by using either FRAP or photoactivation Saxton et al, 1984;Mitchison, 1989;Zhai et al, 1995; WatermanStorer et al, 1998;Cimini et al, 2006). In most studies using FRAP, the data were fit to a single exponential that represented the turnover of the highly dynamic spindle MTs.…”