Fig. 1. Dynamics of EGFR and Dpp signaling in the Drosophila follicular epithelium. (A) Phase contrast image of a stage 10 egg chamber, showing the follicular epithelium (gray), the oocyte (white), the nurse cells (blue) and the stretch follicle cells. (B,C) In situ hybridization images of thickveins (tkv) expression at stage 10B of oogenesis (B, lateral view; C, dorsal view). (D) Schematic of the tkv pattern in a stage 10B egg chamber. (E-G) EGFR activation monitored by the nuclear localization of Capicua (Cic), a transcription factor excluded from the nucleus in response to EGFR signaling. (E) At stage 10A, Cic is excluded from nuclei of the dorsal anterior follicle cells (marked by a dotted white line). (F) At stage 10B, Cic is excluded from the nuclei within a broad patch of dorsal cells (marked by a dotted white line). (G) Dorsal view of a stage 12 egg chamber: Cic is excluded from the nuclei in and around two dorsolateral stripes of the follicle cells. At the same time, nuclear Cic reappears in the triangular patch of the dorsoanterior cells (marked by an asterisk). (H-J) Dpp signaling monitored by the phosphorylated Mad (P-Mad). P-Mad is first detected in the two rows of anterior follicle cells (H). Later, P-Mad is found in a single row of ventral cells, and in at least five rows of dorsal cells (marked by a solid white line) (I). After stage 11, the P-Mad pattern is split along the dorsal midline (J). (K-M) Merged images of Cic (red) and P-Mad (green). In all images anterior of the egg chamber is to the left; the yellow dashed line marks the anterior border of the oocyte; the arrowhead marks the dorsal midline. E,F,H,I,K,L are lateral views, and G,J,M are dorsal views, of the egg chamber. A, anterior; D, dorsal; FC, follicular epithelium; NC, nurse cells; P, posterior; SC, stretch follicle cells; V, ventral.