Fig. 5. Elimination of zygotic fizzy-related expression restores progression through mitosis 16 and induces an extra division cycle in the epidermis of CycA mutants. (A-D) High magnification views of the embryonic epidermis after anti-tubulin labeling (Tub) at stage 12 when epidermal cells are already post-mitotic in wild-type embryogenesis. The reduced cell density resulting from the failure of the terminal mitosis 16 in CycA^C8LR1 mutants (D, CycA^-) is not present in fzr^ie28; CycA^C8LR1 double mutants (C, fzr^- CycA^-), which have the same cell density as sibling control embryos (A, +) and fzr^ie28 single mutant embryos (B, fzr^-). (E-G) High magnification views of the embryonic epidermis after anti-Cyclin B labeling (CycB) at stage 13. Although Cyclin B does not accumulate after mitosis 16 in the post-mitotic epidermal cells of sibling control embryos (E, +), it reaccumulates during an extra division cycle 17 not only in fzr^ie28 single (F, fzr^-) mutants (Sigrist and Lehner, 1997), but also in fzr^ie28; CycA^C8LR1 double mutant embryos (G, fzr^- CycA^-). Cyclin B is also again degraded during the additional mitosis 17 (for examples see arrows in F,G). (H,I) Mitotic figures observed during the additional cell division 17 in fzr^ie28 single (H, fzr^-) and in fzr^ie28; CycA^C8LR1 double (I, fzr^- CycA^-) mutant embryos after anti-tubulin (Tub) and DNA labeling (DNA). Normal prophase, prometaphase, metaphase, anaphase and telophase figures are shown from left to right in H and I. In addition, abnormal anaphase and telophase figures with chromatin bridges were also present in the fzr^ie28; CycA^C8LR1 double mutant embryos, as illustrated by the two right most panels in I.