Interphase progression in cyclin RNAi-treated embryos. (A–D) Video frames of GFP-PCNA (top; white) and histone-RFP (bottom; red) during the thirteenth syncytial cycle. Time is given in minutes and seconds. (A) Control embryos had a short gap phase before mitotic entry (<2 min, between 11:12 and 13:37; Video 1). (B–D) Pairwise knockdown of mitotic cyclins prolonged interphase, mainly by extending the G2 (e.g., ∼6 min between 15:57 and 21:59 in B; Video 2). (E) S-phase duration. Mild prolongations of S phase were observed in CycA+B and CycA+B3 RNAi-treated embryos as compared with the control, whereas treatment with CycB+B3 RNAi had no significant effect. (F) Gap-phase duration. All the combinations of cyclin RNAi treatment extended the gap phase. CycB+B3 RNAi was most dramatic. Error bars represent SDs. n > 3. (G and H) Alexa Fluor 546–dUTP (red) was incorporated into DNA when injected before but not after the dispersal of PCNA foci (green) in CycB+B3 RNAi-treated embryos. Bars, 5 µm.