Cell volume increases transiently during mitosis. (A) Sketch of the thin PDMS chamber filled with fluorescent dextran for volume measurements, cross section of the chamber with the corresponding profile of fluorescence, and images of a cell in phase contrast and fluorescence in gray levels and false colors. Dashed lines on the grayscale image correspond to the sketch and profile on the left and on the color scale image show the integration area for calculation of cell volume. (B) Time-lapse images of HeLa cells in phase contrast and FXm. Arrows correspond to cells whose volume is shown in C. (C) Whole cell cycle volume trajectory, where arrows correspond to cells shown in B. V0, cell volume at birth; VR, volume at rounding; and VM, maximum volume reached during mitotic swelling. Close-up shows the volume overshoot occurring during mitosis (V0S = VM − VR). (D) Time-lapse images of a HeLa cell stably expressing histone H2B-mCherry, in phase contrast, with FXm and in fluorescence for mCherry (Video 1). (E) Absolute volume as a function of time for the HeLa cell and the two daughters shown in D, with a time lapse every 2 min. Colored lines indicate successive mitotic events. (F) Mean volume overshoot for n = 25 mitotic HeLa cells in one single experiment. Time registered at cell mitotic rounding (time = 0), and SEM is shown in gray. (G) Mean volume as in F, with time registered at cell mitotic rounding (time = 0) and normalized for mitosis length (anaphase at time = 1). Mean overshoot is 21.02%, and SEM is shown in gray. (H) Relative volume change in mitosis (V0S = 20.72%, SEM = 0.73, n = 60, N = 2). Bars, 20 µm.
