Prolonged prometaphase and centrosome loss signal through the same components to arrest the cell cycle. (A) Mitotic duration in histone H2B-EGFP–expressing p53^−/−, 53BP1^−/−, and USP28^−/− Plk4^AS cells, grown in either DMSO or 3MB-PP1 for 6 d. Data are means ± SEM (n = 2, >25 cells per experiment). (B) Schematic of the mitotic timer experiment. Graph shows the prometaphase duration and proliferative capacity of 3MB-PP1–treated Plk4^AS cells. Each bar represents a daughter cell; its height represents the prometaphase duration of the mother cell, and its color represents the fate of the daughter. The dashed red line indicates the maximum time that mother cells spend in prometaphase before >85% of daughter cells undergo a cell cycle arrest. (C) Mitotic duration in histone H2B-EGFP–expressing Plk4^AS cells. Measurements were taken over a 24-h period at indicated times after 3MB-PP1 addition. Data are means ± SEM (n = 2, >25 cells per experiment). (D) A model for stress signaling inputs into the mitotic surveillance pathway. *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001.