Grp prevents CycB nuclear accumulation by a Wee1-independent mechanism. (A–C) Wild-type (A), grp (B), and wee1 (C) mutant embryos expressing RLC-GFP (cyan) were injected with a mix of Aph and CHX (CHX + Aph) at metaphase of cycle 12. 5–8 min after the onset of the next interphase, they were injected with 10 mM of the CDK1 inhibitor Roscovitine followed by 13 μM CycB-R (see Videos 9 and 10 for B and C). The schematic describes the injection and imaging sequence. The right column of each panel is an enlargement of the area outlined by the white box in the first images of the left column. Red arrows point to the nuclear localization of CycB-R. Time is given in minutes/seconds. Bars: (left) 20 μm; (right) 5 μm. (D) Histograms indicate the time until CycB-R starts accumulating in at least three nuclei in embryos treated with CHX + Aph and the CDK1 inhibitors Roscovitine or RO-3306. The embryos injected with RO-3306 and Roscovitine were subsequently injected with 56 μM and 13 μM, respectively. Data are represented as mean ± AVD. n, number of embryos injected. *, only 5 out of 10 wild-type embryos injected with Roscovitine showed nuclear CycB-R accumulation before 15 min, which is the time limit of each video for the Roscovitine assay. Therefore, the mean timing of nuclear CycB-R import represents only half of the embryos injected. (E) The table summarizes the results in Figs. 6 and 7. (F) The schematic presents a model for the control of CycB nuclear import. CycB nuclear accumulation is inhibited by Grp and activated by nuclear CDK1 activity, which is itself inhibited by Grp and Wee1.