Fig. 4. Notch-dependent repression of the Cyclin E inhibitor Dacapo is required for mitotic-to-endocycle transition. (A) The dacapo mRNA in situ pattern indicates transcriptional downregulation after transition to endocycles (light arrow, st. 7). (B) A similar expression pattern was observed in a dap5gm construct, which includes the entire gene and a part of the promoter region fused with myc-epitope tag (arrow indicates follicle cells staining prior to st. 7). (C,C') Prolonged follicle cell expression of dap5gm in st. 9 Delta germ line clone shows that dap is controlled by Notch signaling. (D) Overexpression of dap (hsFlp; UAS-dap; UASGFP act<FRT-CD2-FRT<Gal4) inhibits endoreplication: follicle cells overexpressing dacapo have smaller nuclei (D') than the neighboring wild-type cells and they fail to incorporate BrdU during both the endocycling (E,E') and the amplification (F,F') stages, indicating that these cells could not undergo the S-phase and probably are blocked at the G1/S transition. Green, GFP (C,D), BrdU (E,F); red, CycE (D), Dap (E,F); blue, DAPI.