Fig. 7. Ed acts in the signal-receiving cells. (A) Nrg derivatives: Nrg¹⁸⁰ is the full-length neuron-specific protein isoform and contains the Nrg extracellular, the Nrg transmembrane (TM) and the Nrg¹⁸⁰ intracellular domain. Nrg^GPI contains only the Nrg extracellular domain and is anchored to the plasma membrane by the Fasciclin 1 GPI moiety (Hortsch et al., 1995). (B) Ed derivatives: Ed contains the complete extracellular and TM Ed domains, followed by the entire 315 amino acid intracellular Ed domain. Ed^Dintra lacks the intracellular Ed domain. Ed^C50 contains the Ed TM domain and the last C-terminal 50 amino acid of Ed. (C-E) Scanning electron micrographs of adult eyes. (F-K) Eye discs stained for the photoreceptor marker ELAV (red, F-H) and cone cell marker Cut (green, I-K). (C,F,I) GMR-GAL4/UAS-nrg^GPI; (D,G,J) GMR-GAL4/UAS-ed/UAS-nrg^GPI; (E,H,K) GMR-GAL4/UAS-ed^C50. (I-K) Upper focal planes of (F-H), respectively. Overexpression of nrg^GPI (C,F,I) alone causes no apparent phenotype at 25°C. However, co-expression of both ed and nrg^GPI results in a severe rough eye phenotype (D). A similar phenotype is induced by the overexpression of ed^C50 (arrows in H,K). Arrows in G,J indicate ommatidia contain fewer photoreceptor and cone cells, respectively.