Drug-induced microtubule depolymerization events in real time. (A) Control (no drug) experiment of stable U2OS cells with the red tyrosination sensor; microtubule dynamics are indicated with yellow, white, blue, and green arrowheads. (B–D) Movie frames of stable U2OS cells with red tyrosination sensor treated with nocodazole, colchicine, and vincristine (two rows). The depolymerization and severing events are indicated with colored arrowheads and asterisks, respectively, for each panel. Full movie of the frames can be found in Videos 3–6 for A–D, respectively. Scale bars = 5 µm, and time in minutes:seconds (as indicated). (E) Quantification of microtubule dynamic instability (blue, characterized by a filament undergoing both catastrophe and growth event in the given time frame of the movie), polymerization (green, characterized by a continuous microtubule growth in the given time frame of the movie) and depolymerization (red, characterized by a continuous catastrophe event in the given time frame of the movie) events respectively, from the movies ranging from 5 to 45 min analyzed for control and drug-treated experiments (Materials and methods). Data derived from two to four independent experiments n = 100 events for each. (F) The number of microtubules where both the ends are visible, a proxy for microtubule severing events observed for control and drug-treated experiments. Data are derived from two to four independent batch of cells treated with drugs and averaged from five different cells; error bars represent SEM. MT, microtubule.