Mitotic swelling is independent of actin cortex integrity and contractility and is accompanied by a drop in cell density. (A) Images of LifeAct-mCherry HeLa cells treated with 5 µM latrunculin A and MYH9-GFP HeLa cells treated with 80 µM ROCK inhibitor Y27632. Bars, 20 µm. (B) Relative mitotic volume change for HeLa cells treated with latrunculin A (red) and Y27632 (green), with three types of controls: untreated cells (CRTL), addition of DMSO only, and cells in nonadherent chambers with DMSO. (C) Images of an HT29 cell undergoing mitosis with FXm and dry mass density imaging. Bars: (top) 20 µm; (bottom) 24 µm. (D and E) Volume and dry mass for the cell in C. (F) Density of the cell in C calculated from the volume and dry mass. (G) Mean volume and dry mass in mitosis for HT29 cells. Volume and mass are normalized to 1 and time is set to 0 at volume overshoot start, and time is set to 1 at the end of the overshoot (D–F, dashed line). Light blue and red areas show the SD for volume and mass, respectively (n = 8 for G ). (H) Mean cell density for HT29 cells, where time is set to 0 and 1 at volume overshoot start and end, respectively. The SD is shown as the gray area.