Fig. 1. The roulette mutant is an allele of the Egfr-ligand argos. Panels show eye imaginal discs (A-C) or adult eye sections (D-I). Anterior is left and dorsal up. (A) Eye-imaginal disc stained with anti-Elav (red, all photoreceptor precursors) and m0.5-lacZ (blue, R4 precursors) shown as an overlay with a Nomarski optics bright-field view of same disc. The dorsoventral midline, equator (Eq), is marked by white broken line, the position of the morphogenetic furrow (MF) is indicated. (B) Higher magnification of boxed area from A also showing anti-Boss (green, marking the central R8 cell in each cluster). Note regular arrangement and orientation of ommatidial clusters. Overlay of the red and blue channels is for clarity shown in blue. (C) Semi-schematic presentation of ommatidial rotation (generated from real clusters shown in A,B with the `solarize' filter of Adobe Photoshop). Representative clusters for the dorsal and ventral halves are shown. Colors are as in B. R3/R4 photoreceptor precursors are indicated by white numbers. Ommatidial preclusters represent examples from columns 4, 5, 7, 9, 12 and 15, respectively. Yellow arrows indicate rotation of clusters. The rotation angle of individual clusters is indicated above the panel. The `base' of arrows indicates the R3/R4 axis and the arrowheads point towards the middle of cluster. Note successive changes in the rotation angles to the complete 90°. (D) Examples of mature adult ommatidia with numbered photoreceptor rhabdomeres (R1-R7; R8 is below the plane of section) and schematic arrows as shown in E-I. Black arrow: dorsal ommatidium; red arrow: ventral ommatidium. (E-I) Tangential sections of equatorial region of adult eyes with schematic presentations below sections. (E) wild-type (wt), (F) argos-roulette (aos^rlt/aos^rlt), (G) aos^rlt/aos⁷, (H) aos^rlt/Df(3L)st7P, (I) sev-aos/+; aos^rlt/aos^rlt. Note that aos^rlt fails to complement aos alleles and that sev-aos fully rescues the aos^rlt phenotype. Ommatidia with a wt photoreceptor number are represented by arrows with flags; clusters with extra photoreceptors are indicated by simple arrows.