Fig. 4

Visualization and quantification of F-actin and mitochondrial distributions in dividing HeLa cells. HeLa cells were transfected with GFP-UtrCH and stained with MitoTracker Deep Red FM to visualize F-actin (shown in green) and mitochondria (shown in magenta) respectively then imaged by spinning disk confocal microscopy. a Representative time-lapse images of a dividing HeLa cell showing F-actin and mitochondrial enrichment at the cell equator and depletion at the cell poles as division proceeds. Images are maximum projections of five z-slices from the centre of the confocal stack. Green and magenta arrowheads indicate F-actin and mitochondria localized to the cell equator respectively. Blue arrowheads indicate mitochondria colocalized with F-actin at the cell equator. Red arrowheads indicate enriched F-actin in the subcortical regions of cytokinetic cells. Bar, 10 μm. b Quantification of mitochondrial and F-actin fluorescence intensity from cell pole to cell equator at five representative stages of division. The normalized distance from cell pole to equator is displayed on the x-axis and the average fluorescence intensity normalized against the mean is displayed on the y-axis. Data were represented as mean ± SEM (8 cells, N = 32) and lines were fitted by non-linear regression. The polarization of mitochondria and F-actin towards the cell equator was statistically significant relative to metaphase from anaphase onwards (F-Test, p < 0.05). c Average equator: pole fluorescence intensity ratios (y-axis) were plotted against time following metaphase exit (x-axis) for both mitochondria (magenta line) and F-actin (green line) from metaphase exit (t = 0 min) to late anaphase (t = 5 min). Data were represented as mean ± SEM (8 cells, 4 quadrants; N = 32). The black arrow indicates the onset of mitochondrial and F-actin polarization towards the cell equator