Figure 4.

Regulators of microtubule dynamics affect congression, tension, and spindle length, but do not exert their influence via flux. (A) Spindles of RNAi-treated cells were immunostained for the centromere marker, Cid (red), in order to measure chromosome congression on spindles. Microtubules, green. Scale bar, 2 μm. (A′) Congression was evaluated by the average centromere displacement from the spindle equator, expressed as a percent of the pole-to-pole spindle length. Notably, some treatments that perturb flux rate (RNAi of KLP10A or KLP67A, or co-RNAi of Msps/KLP10A) do not inhibit congression. (B) Interkinetochore tension was evaluated by measuring the distance between sister centromeres immunolabeled with Cid antibody. Yellow arrowheads mark one pair of Cid-immunostained sister centromeres on a control metaphase spindle. (B′) Average distance between sister centromeres after RNAi to knockdown the indicated target proteins. Note that some RNAi treatments (specifically, Mast or KLP10A) decrease flux but fail to significantly decrease centromere spacing. (C) Average pole-to-pole spindle lengths after RNAi to deplete the activities of the indicated regulators of microtubule dynamics. A number of treatments significantly decrease flux but have no significant effect on spindle length.