Fig. 3. The Cyclin E levels are dynamic during cell cycle transitions; constant CycE levels halt endocycles and amplification. (A) Wholemount in situ hybridization indicates equal level of cyclin E mRNA in the follicle cells throughout oogenesis (arrows). (B,C) Cyclin E antibody staining pattern (green) between stages 5 (B) and 8 (C) shows a clear downregulation of the protein after the transition to the endocycle, when cells stop expressing PH3 (red). Cells overexpressing CycE (hsFlp;;UAS-cycE/UASGFP act<FRT-CD2-FRT<Gal4) express mitotic cyclins B and A past stage 6 in oogenesis (D-E, arrow), have smaller nuclei (F,F') and show highly reduced BrdU incorporation during endocycling (G,G') and amplification (H,H') stages, suggesting that cells ectopically expressing cyclin E fail to undergo S-phase and are halted at G2. Green, CycE (B,C), GFP (D-F), BrdU (G,H); red, PH3 (B,C), CycB (D), CycA (E), CycE (F-H); blue, DAPI.