Fig. 6. Notch activation in R1/R6s represses both Svp and Sens expression. L3 eye discs. Images are all from the apical region of the disc, containing the R3/R4 and R1/R6 nuclei (labeled in A), and the R7 nuclei (asterisks) but not the R8 nuclei; all panels are presented in the same orientation. Images are from rows 15-17. (A-B') Wild-type or sev-N^act L3 eye discs were stained with antibodies against Sal (green), Svp (red) and Sens (blue). (A,A') In wild-type L3 eye discs, R7s express Sal, R1/R6s and R3/R4s express Svp, and R8s (not shown) express Sens. (B,B') The sev-N^act transgene expresses the intracellular domain of N in R1/R6s, R3/R4s and R7s. R1/R6s expressing activated N lose Svp expression and, like svp mutant R1/R6s, gain Sal expression. Unlike svp mutant R1/R6s, they never express Sens. (Activated N does not affect Svp expression in R3/R4s.) (C-D'') sev-N^act or sev-N^act; svp mutant L3 eye discs were stained with antibodies against Pros (green), Elav (red) and Sens (blue). (C-C'') All R1/R6s expressing activated N gain Pros expression but never Sens, consistent with adoption of the R7 fate (compare with wild-type R1/R6s in Fig. 5C). A small number of R1/R6s gain Pros but also lose the neuronal marker Elav, consistent with adoption instead of the cone cell fate (arrow). R3/R4s gain neither Pros nor Sens expression, consistent with their continued expression of Svp and failure to express Sal (see B,B'). (D-D'') In svp mutant L3 eye discs, R1/R6s (solid circles) expressing activated N always express Pros and not Sens. Activated N does not affect the ability of svp mutant R3/R4s (dashed circles) to express Sens. Scale bar: 5 µm.