Figure 5.

Nuclear Cyclin B1 can drive mitosis in Cyclin B1^−/− embryos. (A) Frames of Video 10 are shown from the eight-cell stage onwards. Synthetic mRNAs encoding nuclear Cyclin B1 and H2B-RFP were injected in one blastomere at the two-cell stage. The uninjected half of the embryo is to the right of the dotted line, the injected half of the embryo divides up to the 16-/32-cell transition. Top row shows the channel merge of a single central plane through the embryo. Middle row shows projection of the H2B-RFP channel. Bottom row shows projection of the nuclear Cyclin B1 channel. (B) Comparison of rescue efficiency of wild-type (wt; blue, n = 51) and nuclear Cyclin B1 mRNA (red, n = 31, eight independent experiments) in driving Cyclin B1^−/− embryos beyond the arrest stage (left). Comparison of the number of divisions that wild-type and nuclear Cyclin B1 can promote in Cyclin B1^−/− embryos (right). Bar, 20 µm.