Cyclin-type effect on interphase timing. (A) As illustrated for RNAi knockdown of CycA (A) and CycB3 (B3), after pairwise cyclin knockdown, the dose of the remaining cyclin (CycB, B) did not significantly affect interphase length (McCleland et al., 2009b). Halving the gene dose of the remaining cyclin (performed for all combinations) had a minimal effect on interphase length (comparison on the left), arguing that cyclin level is not a major determinant of interphase length in these conditions. In contrast, the type of cyclin remaining (comparison on the right) influences interphase duration (this study). (B and C) Real-time records of histone (RFP-H2AvD) and centrosomes (GFP-TACC) show that RNAi against CycB+B3 (C), which created a situation in which the cell cycle was running mainly on CycA, greatly extended the interphase length in cycle 13 compared with the control (B; 28:12 vs. 13:46 [minutes and seconds]). Bar, 10 µm. (D) Interphase durations in control and each of the pairwise cyclin knockdown embryos. Mean interphase 13 length was 12.02 ± 0.92 min in control embryos, whereas knockdown of CycA+B, CycA+B3, or CycB+B3 extended interphase to 19.19 ± 1.57, 16.76 ± 1.67, or 24.81 ± 1.75 min, respectively (±SD). Horizontal lines show means.