Pericentrin is critical for proper spindle elongation in two-centrosome cells. (A) Time-lapse observation of the structure of microtubules upon depletion of pericentrin. HCT116 cells were observed with a 40× objective. Gray represents SiR-tubulin. Z-projections: 10 planes, 2.2 µm apart. Scale bar, 10 µm. Time zero corresponds to mitotic onset. (B) Averaged time courses of the pole length at each time point in A. The length between two poles of spindle was measured from 40 cells from two independent experiments. Time course data were aligned at the time of the mitotic onset (0 min). Error bars represent SD. (C) Mitotic spindle structures of two-centrosome RPE1, GI1, SKOV3, A431, and PANC1 cells. Red and blue represent α-tubulin and DNA, respectively. Z-projections: 31 planes, 0.5 µm apart. Scale bar, 10 µm. (D–H) Quantification spindle length (n > 40 from two independent experiments) in C. Line and error bars represent the mean and SD. The Mann–Whitney U test (two tailed) was used to obtain a P value. *, P < 0.0005. n.s., not significantly different.