(A) Addition of recombinant kif2a to stage 3 extracts decreases spindle size in a dose-dependent manner. Mean ± SE, n ≥ 48 spindles from two extracts, p<0.0001 by Kruskal–Wallis test. Scale bars represent 10 µm. (B) Addition of recombinant importin α to stage 8 extracts increases spindle size. Mean ± SE, n ≥ 86 spindles from three extracts, p<0.0001 by Kruskal–Wallis test. (C) Addition of 1 µM recombinant importin α to steady-state spindles in stage 8 extracts decreases kif2a recruitment to spindles in addition to increasing spindle size. Left panel: Line scan quantification of immunofluorescence intensity with normalized spindle lengths for statistical analysis. Right panel: t-test analysis across each length bin. Black dashed line is equivalent to a p value of 0.01 and red dashed line is equivalent to a p value of 0.001. Mean ± SE, n ≥ 44 spindles from three extracts. (D) Addition of recombinant kif2a can rescue the increased spindle size caused by importin α addition in stage 8 extracts. An NLS mutant of kif2a (kif2a ΔNLS) is more robust at returning spindles to normal size. Mean ± SE, n ≥ 55 spindles from two extracts.