Figure 5: Embryos round up at NEBD following a Myosin-II-dependent cortical tension increase.

(a) Embryo before and during the first mitosis. One Z-plane is shown every 1 h. Scale bar, 10 μm. (b) Graph bar showing the shape ratio (see Methods) of embryos before and during mitosis. Mean is shown of 28 embryos from 10 independent experiments. s.d. is plotted on each bar. Statistical significance of differences is assessed with a Mann–Whitney test (P value <0.0001). (c) Embryo observed by transmitted light (upper panel) expressing SF9–GFP (Myosin-II intrabody, blue: lower intensity, orange: higher intensity). One Z-plane is shown every 1 h. Scale bar, 10 μm. (d) Bar graph showing the ratio between the average intensities of cortical versus cytoplasmic Myosin-II in embryos expressing SF9–GFP 1 h before NEBD, at NEBD or during mitosis. For each embryo, six measurements were taken in the cortex and six in the cytoplasm (see Methods). Mean of 16 embryos 1 h before NEBD, 19 at NEBD and 16 mitotic embryos is shown assessed over 6 independent experiments. S.e.m. is plotted on each bar. Statistical significance of differences is assessed with a t-test (P values: 1 h before NEBD/NEBD 0.1854; NEBD/mitotic 0.1066; 1 h before NEBD/mitotic 0.0013). (e) Control embryo at the Pronucleus stage (left panel) or during mitosis (right panel) stained for chromosomes (magenta, Z-projection is shown over 25 μm) and PhosphoMyosin-II (green, one Z-plane is shown). Scale bar, 5 μm.