Figure 4

Pros is necessary and sufficient for high pERK levels. (A,B,D-G) Eye imaginal discs from control (A,E), pros¹⁷mitotic clones (B,F) and sev>Pros eyes (D,G) were immunostained for Pros (A,B, green; E,G, magenta), pERK (A,B,D, magenta), and Yan (E,G, green; F, magenta). GFP was used to mark wild-type (versus pros¹⁷mutant) tissue (B,F, green), and nuclei were visualized with DAPI (E,F,G, blue). (C) A diagram representing Pros regulation by Ras/MAPK signaling previously reported [26, 27, 29], and the positive feedback onto pERK described here. In optical sections at the level of the R7 and CCs, high Pros expression correlates with high pERK expression (A,C, arrows), whereas a cell autonomous reduction in pERK is observed in pros mutant tissue (B, non-GFP positive cells). No change in pERK is observed in more basal optical sections where Pros is not expressed (data not shown). (E) In wild-type imaginal discs, Yan expression (green) becomes reduced as Pros expression (magenta) increases in specified CCs. (F) In pros mutants, Yan (magenta) is only present in nuclei in GFP-negative (that is, pros-negative) tissue, whereas it is both nuclear and cytoplasmic in surrounding GFP-positive wild-type tissue (green). (G) In sev>Pros imaginal discs, Yan (green) is reduced throughout the disc, being almost undetectable in cells expressing particularly high levels of Pros (magenta).