Fig. 2. Delta signals from the germline cells to regulate the transition from mitotic cycle to endocycle in follicle cells. (A) Delta expression is upregulated at stage 6 and reaches its highest at stage 7 in the germline cells (green). This upregulation is coincident with the cell cycle transition (Phospho-Histone 3 staining in red is observed in stage 6 (arrows), but not in stage 7 egg chambers). (B) Delta is not required in the follicle cells for the transition, as no extra cell divisions were observed in Dlrev10 follicle cell clones (PH3, blue in B). (C,D) Delta is required in the germline, as Phospho-Histone 3 (PH3, blue in C, arrows) and Cyclin B (Cyc B, red in D, arrows) are observed in follicle cells of stage 8 and 9 egg chambers carrying germline clones of Delta. Green in B-D shows GFP, which marks the wild-type cells, and cells that lack GFP expression are mutant clones. Epithelial polarity is normal in these egg chambers based on normal Armadillo localization (red in B,C). In later egg chambers, some epithelial defects were observed (data not shown).
