Fig. 3. Iro-C promotes and organizes Drosophila eye growth. (A) The three Iro-C genes are expressed in the dorsal (D) half of the eye disc (Iro-C domain). This expression is necessary to establish the eye DV organizer (thick horizontal black line). Iro-C represses within its domain the expression of fng and the apposition of ventral (V) fng-expressing and D non-expressing cells allows the activation of the N receptor at this interface. N activity is essential for eye growth and patterning, but the nature of the signals (arrows) downstream of this activity are unknown. Iro-C^- clones within the Iro-C domain allow expression of fng and establish ectopic organizers that promote development of ectopic eyes. (B,C) Conventional optic and confocal view of an eye-antenna disc bearing an Iro-C^- clone (asterisk and outlined in red or white) on which the drawing in A has been modelled. (C) In the confocal view, the developing extant and ectopic eyes are visualized by Elav staining (green or yellow) that reveals developing photoreceptors. White arrowheads show positions of eye DV axes of symmetry. mf, morphogenetic furrow. (D) Ectopic eye (arrowhead), which results from an Iro-C^- clone like the ones shown in B,C. (Data taken from Cavodeassi et al., 1999.)