Fig. 6. Model for integration of AP and DV positional information and eggshell patterning. (A) Cartoon depicting a lateral surface view of a stage 10B egg chamber. A single appendage primordium (green) is shown. Cic is downregulated in dorsal follicle cells, allowing Dpp to induce mirr expression; dorsally-localized Egfr activation also positively regulates mirr independently of Cic. Cic remains present in the remaining follicle cells and prevents the induction of mirr by an anterior positional cue, probably Dpp. (B) Diagram of an anterior cross section through an egg chamber, illustrating the follicular epithelium (shaded outer section) surrounding the oocyte (inner large circle). The oocyte nucleus (gray circle in oocyte) marks the dorsal side. Cic (dark brown) is lost from dorsal follicle cells where Egfr signaling exceeds a certain threshold, rendering these follicle cells competent to express mirr and adopt an appendage-producing fate (green), and thus defining the ventral limit of the appendage primordia. As proposed previously (Wasserman and Freeman, 1998), Aos (red) is induced in dorsalmost follicle cells in response to higher levels of Egfr activation (circles), resulting in local downregulation of Egfr activation and generating a dorsal midline fate (light brown) that marks the dorsal limit of the appendage primordia.