CycB drives cytoplasmic mitotic events independently of the nuclear cycle during cellularization. (A) CycB is limiting for nuclear and cytoplasmic CDK1 activity when injected at the onset of cycle 14 interphase. An RLC-GFP embryo was injected with CycB at cycle 14, 3 min after NEF. The arrowhead marks the site of injection. At the site of injection, RLC-GFP disappeared from the cortex 5 min after injection (blue outlines). NEB occurred 5 min later (orange outline; see Video 4). Time is given in minutes/seconds. Bar, 20 μm. (B) CycB drives the cytoplasm but not the nuclei into mitosis when injected later during interphase of cycle 14. RLC-GFP, GFP-moesin (see Video 5), and GFP-Nuf embryos were injected with CycB at cycle 14, 8 min after NEF. Arrowheads mark the sites of injection, and blue outlines mark the areas where the cytoplasm entered mitosis. Time is given in minutes/seconds. Bars, 20 μm. (C) The timing of cytoplasmic and nuclear CDK1 activation was determined as described in Fig. 2. Data are represented as mean ± AVD. n, number of embryos injected.