Mechanical spindle relaxation time correlates to metaphase duration. (a) Drosophila melanogaster brain tissue before and after ISI. A rectangular ROI is used to generate guided kymographs from which flux velocity is calculated. Bars, 5 µm. (b) MT poleward flux velocity (F) versus spindle length (2L). Center and semi-axes of the shaded ellipses correspond to the mean and SD of the data point cloud for each cell type. (2L ± SD, F ± SD, n), Ganglion mother cells (6.4 ± 1.0 µm, 0.8 ± 0.4 µm/min, n = 27 cells); ovarian follicles (6.8 ± 1.4 µm, 1.7 ± 0.3 µm/min, n = 10 cells); neuroblasts (12 ± 2.6 µm, 1.4 ± 0.5 µm/min, n = 8 cells); and S2 cells (9.8 ± 1.2 µm, 1.0 ± 0.4 µm/min, n = 15 cells). (c) Metaphase duration (τ_meta) matches relaxation time (τ_relax = L/F) across cell types, meaning that time is allowed for ≈1 flux-driven translocation cycle along the half-spindle (green cone) before anaphase onset. Relaxation time is obtained from the data points in panel b, through τ_relax = L/F. Metaphase duration is, for Ganglion mother cells: 3.3 ± 1.3 min, n = 9; ovarian follicles: 1.9 ± 0.7 min, n = 7; neuroblasts: 5.9 ± 2.2 min, n = 9; and S2 cells 5.5 ± 3.2 min, n = 22. (*) A Drosophila embryo (cycles 11–13) data point is added by collecting data from the literature for the three parameters involved: τ_meta = 2.5 min (Minden et al., 1989); 2L = 12 µm (Brust-Mascher et al., 2009); F = 2.6 µm/min (mean value of available data; Brust-Mascher and Scholey, 2002; Brust-Mascher et al., 2004, 2009; Rogers et al., 2004; Wang et al., 2010).