RNAi of individual and pairwise combinations of mitotic cyclin disrupt mitotic progression. (A) Embryos expressing histone-GFP were injected with the indicated dsRNA and followed in real time from mitosis of cycle 11 to the beginning of cycle 14. Mean times for mitosis 13 are presented. The beginning of prophase was defined by the onset of chromatin condensation, and metaphase was defined by the complete alignment of chromosomes until anaphase onset. The asterisk indicates absence of metaphase. Error bars represent SD. (B) Model for coupling mitotic events to cyclin function and destruction. The three mitotic cyclins are temporally degraded within mitosis: CycA before metaphase, CycB at the metaphase–anaphase transition, and CycB3 during anaphase. Our cyclin RNAi experiments suggest that each cyclin has a specialized function for distinct mitotic steps. Coordinating cyclin function and destruction may guide mitotic progression.