Fig. 6. Survivin is required for checkpoint arrest in response to taxol. (A,B) Phase-contrast images of cells from cultures transfected with control or Survivin siRNAs that were blocked in S-phase, released in medium supplemented with 33 nM taxol (A) or 0.1 µg/ml nocodazole (B) and followed every hour after entering mitosis for 8 hours. Arrows, arrowheads or asterisks indicate individual cells of interest. (C) Histogram showing the percentages of cells from cultures transfected with control (C) or Survivin siRNAs (S) that either arrested in mitosis (yellow) or exited into interphase (green) in the above experiment. (D-G) Immunofluorescence staining of cells treated as in Fig. 6A,B, stained for Aurora-B (green), DNA (blue), BubR1 (greyscale in D',E',F',G', red in D",E",F",G") and Mad2 (green in D",E",F",G"). Survivin-depleted cells (as judged by Aurora-B staining) show no little or no staining for BubR1 or Mad2 at the kinetochores in the presence of taxol. In the presence of nocodazole, Mad2 staining is present at the kinetochores of both control and Survivin-depleted cells, whereas BubR1 is either greatly depleted or absent. Bar, 5 µm.