Figure 1

R7s lacking Sce , Scm , or Pc adopt an R8-like fate. (A,B) Medullas from adult mosaic animals. Homozygous R7 clones generated by GMR-FLP/MARCM express GFP (green). All R axons are labeled with mAb24B10 (red). Scale bar is 5 μm. Wild-type R8 axons terminate in the M3 layer (upper dashed lines) whereas wild-type R7 axons terminate in the M6 layer (lower dashed lines; [28,29]). (A) All wild-type (homozygous FRT82) R7 axons terminate in M6, the R7 target layer. (B) 38.4% ± 9.4% (n = 3 brains) of Sce mutant R7 axons terminate in M3, the R8 target layer (arrow). A further 7.6% ± 3.4% terminate between the M3 and M6 layers (arrowhead). (C–F') Representative adult mosaic ommatidia containing homozygous R7s (green, arrows) generated by GMR-FLP/MARCM. Stained with antibodies both against the R1-R6-specific rhodopsin Rh1 (red) and against either the R7 rhodopsins Rh3 and Rh4 (C–D'; blue) or the R8 rhodopsins Rh5 and Rh6 (E–F'; blue). Scale bar is 5 μm. (C,C') Wild-type (FRT82) R7s express Rh3 or Rh4 rhodopsins. (D,D') Many Sce mutant R7s lack Rh3 and Rh4 rhodopsins. (E,E') Wild-type (FRT82) R7s lack the R8-specific Rh5 and Rh6 rhodopsins. (F,F') Many Sce mutant R7s express either Rh5 or Rh6 rhodopsin. (G) Quantification of R8 rhodopsin expression by homozygous Sce, Scm, Pc, or Psc mutant R7s in adults. Error bars represent SEM. 38.8% ± 4.4% (n = 10 retinas) of Sce, 23.8% ± 8.5% (n = 4 retinas) of Scm, and 6.37% ± 3.0% (n = 4 retinas) of Pc mutant R7s express Rh5 or Rh6. We never observed homozygous wild-type or Psc mutant R7s expressing Rh5 or Rh6 and also found that 0/1,090 (n = 4 retinas) Sce/+ and 0/1,150 (n = 4 retinas) Scm/+ R7s expressed Rh5 or Rh6.