Fig. 7. Ectopic activation of Notch can induce extra polar cells. Arrows indicate polar cells. (A-C) Flip-out clones expressing fng marked with GFP (green) and stained for expression of A101 (ß-galactosidase, red). (A) Stage 4 follicle with three polar cells. (B) Stage 8 follicle with ectopic fng expression including the posterior polar cells, only two polar cells form. Inset shows A101 expression for the boxed region. (C) Stage 10A follicle with ectopic fng expression in follicle cells adjacent to the posterior polar cells, only two polar cells form. (D) X-gal stain of stage 3 wild-type follicle with E(spl)mß-lacZ expressed specifically in the polar cells. (E) Stage 5 follicle with Flip-out clones expressing activated Notch, marked with GFP and stained for Fas III (red). Three polar cells form (arrow). Lateral follicular cells also express activated-Notch, but are not transformed into polar cells.