FIG. 6.

In vivo checkpoint studies. Third-instar larvae were fed for 2 h on instant food with or without a drug (or irradiated and then left for 2 h). (A) Aphidicolin or hydroxyurea; (B) etoposide or UV irradiation; (C) caffeine; (D) colchicine. The larval brains were dissected, and the MI was determined after DAPI staining. The MIs were normalized to the MI for untreated brains in each case. Whereas wild-type neuroblasts respond as expected to perturbation of the cell cycle (arresting prior to mitosis in response to inhibition of DNA replication or DNA damage or in mitosis after spindle depolymerization), DmRfc4 mutant neuroblasts are unable to respond properly to inhibition of DNA replication or induction of DNA damage, although the kinetochore attachment checkpoint can be activated. While caffeine appears to have no effect on either wild type or l(3)Rfc4^e20 neuroblasts, l(3)Rfc4^a18 cells respond by arrest or delay in mitosis, as evidenced by an increased incidence of PCC-like figures.