Fig. 4

Cell cycle re-entry is delayed in cells overexpressing mei-41. (a) The indicated kinase or the lacZ control was overexpressed in the posterior compartment of wing imaginal discs using en-Gal4-GFP. Third instar larvae of the given genotypes were irradiated with 40 Gy and allowed to recover for one, four and six hours (1 h, 4 h, 6 h aIR) respectively, before dissection of the wing imaginal discs. Mitotic cells are highlighted by Phospho-Histone H3 antibody staining (red). GFP labelling was used to determine the antero-posterior boundary (indicated by the dotted line). IR-stress caused a cell cycle arrest, only few cells appear in M phase one hour after irradiation. Entry into mitosis reappears with time in the control (enGFP::lacZ), as well as in the anterior compartment of all genotypes as DNA damage response proceeds. Not so in the posterior compartment, though, where either mei-41 or lok is overexpressed. However, overexpression of grp allowed the cell cycle to resume 6 h post-IR. Size bar represents 100 μm in all panels. (b) Quantification of PH3 signals in the posterior compartment reveals no significant difference amongst the different genotypes 1 h after irradiation (aIR). Re-entry into mitosis is observed in the wild type but not the other genotypes at 4 h aIR. Even at 6 h aIR, significantly less mitotic cells are observed in the posterior compartments overexpressing either mei-41 or lok, whereas grp overexpression had only minor lasting effects. *** p < 0.001; ** p < 0.01; * p < 0.5; ns, not significant) according to ANOVA two-tailed Tukey-Kramer approach for multiple comparisons. Bars represent standard of the mean (SEM). At least 16 wing discs were analyzed for each genotype and time point