Fig. 1. roe loss-of-function causes defective ommatidial cell recruitment. (A-C) Tangential eye sections with anterior leftwards and dorsal upwards. (A) Wild-type adult eye. Outer photoreceptors (R1-6) and the inner R7 are found in every ommatidium (R8 is in a different plane) surrounded by pigment cells (rhabdomeres are numbered in inset). (B) rn¹⁶/rn²⁰ mutant eye with most ommatidia containing fewer R-cells and irregular spacing. (C) Mosaic eye bearing rn¹⁶ clones (absence of pigment). roe^- ommatidia show a reduced number of R1-R6 cells and often multiple R7s (examples indicated with yellow arrowheads; see Fig. S1 in the supplementary material). There are also defects in spacing (example marked by asterisk). (D-E') Areas posterior to the MF in 3rd instar eye discs (anterior is leftwards) stained for -Elav (red, marking all R-cells), -Boss (turquoise in D, marking R8) and -Pros (blue in E,E'; marking R7). (D) rn¹⁶ mutant disc; (E,E') mosaic discs with wild-type tissue marked by arm-lacZ (green in E, outlined in E'). Fewer R cells are recruited per ommatidium. Spacing defects result from the presence of fewer R8 founder cells (examples highlighted by asterisks, see also Fig. 2A,A'). -Pros labels R7 cells (and cone cells in a different plane, which are Elav negative). The multiple R7 phenotype is observed inside mutant tissue (example indicated by yellow arrowhead; wild-type clusters with a single R7 are indicated by arrows). Only the nuclei of R7, R3 and R4 are visible in this focal plane in most clusters. (F) Graph showing the frequency of individual mutant R cells in mosaic ommatidia with a wild-type wt phenotype (random frequency reflecting no requirement is 0.5; n=152 in nine eyes analyzed). R1 and R6 show a significantly reduced frequency, indicating a functional requirement of roe in these cells. (G,H) Pupal retinae stained with -Arm, which delineates cell membranes: (G) wild type (`c' marking cone cells and `1' primary pigment cells in example) and (H) rn¹⁶ are shown. The quasi-crystalline lattice of wild-type pupal eyes is severely disturbed in roe mutants. Cone cell, secondary and tertiary pigment cell, and interommatidial bristle numbers are reduced compared with wild type.