Fig. 4. (A,B) Expression of sev-GAL4, visualized by crossing to UAS-lacZ and staining for anti-ß-gal (green), in relation to Elav (red) expression. Expression of sev-GAL4 commences posterior to the morphogenetic furrow in subsets of photoreceptors, as evident by the overlap with Elav. In addition, sev-GAL4 expression is observed in cells adjacent to the developing photoreceptors, most likely corresponding to mystery and cone cells. (C,D) Misexpression of rn (C) in UAS-rn/+;GMR-GAL4/+ and roe (D) UAS-roe/+;GMR-GAL4/+ both lead to disruptions in the morphology and size of the adult eye. These include an apparent loss of pigment cells and bristle cells, as well as the presence of patches of necrotic tissue (black).