Fig. 3. Overexpression of Roe phenocopies N loss-of-function phenotypes and represses N target genes during eye development. (A,A') roe overexpression clones (marked by GFP in green, outlined in A') in third instar eye disc cause recruitment of supernumerary photoreceptors (anti-Elav, magenta), similar to N pathway loss-of-function clones (compare with Fig. 5E). (B) Tangential section of adult eye of the genotype sep^GAL4, UAS-roe with schematic shown on the right (black and red arrows represent the two chiral forms; green arrows represent symmetrical clusters; black dot shows loss of R cells). Increased levels of Roe expression in R3/R4 precursors often cause the formation of symmetrical R3/R3 type ommatidia (some R4/R4 type are also observed; quantified in C). (C) Quantification of the phenotypes of sev-driven expression of roe, N^ECD and together. Ectopic expression of N^ECD causes a high number of R4/R4-type symmetrical ommatidia and R-cell loss, while Roe causes mostly R3/R3-type and occasional R-cell loss. The N^ECD phenotype is antagonized by Roe co-expression and a reversion to a significant percentage of R3/R3-type ommatidia typical of Roe overexpression is observed (the `loss of R-cell' phenotype is enhanced, see text for details). Total number of ommatidia scored was 391 (roe), 545 (N^ECD) and 329 (roe + N^ECD) with at least three eyes per genotype analyzed. (D,D') Third instar eye disc bearing clones of cells expressing two copies of sep^GAL4, UAS-roe (marked by absence of Ubi-GFP in green, see Materials and methods). Expression of the R4-specific N reporter m-lacZ (red) is largely suppressed inside the Roe-overexpressing tissue. Cells outside the clone can be either wild type or have one copy of sep^GAL4, UAS-roe, which can also suppress m-lacZ to a lower extent (not shown). -Elav is in blue.