Fig. 4. PB inhibits EY function post-transcriptionally. (A) Targeted expression of PB in eyes represses the EY regulatory pathway, but does not affect ey transcription. In situ hybridization (parts 2,7), ß-galactosidase staining (parts 3,8) or immunostaining (parts 4,5,9,10) were performed on wild-type (parts 2-5) or dpp-Gal4; UAS-PB (parts 7-10) third instar eye antenna imaginal discs. Adult heads of wild-type or dpp-Gal4; UAS-PB are shown in (parts 1 and 6). (B) Model proposed to explain PB-dependent EY inhibition. Ectopic eye induction, and consequently activation mediated by ey, is inhibited by PB (C). Targeted expression of PB, EY or both proteins with dpp-Gal4 driver. PB led to eye inhibition and leg and wing defects (C1), whereas ectopic eyes were induced by EY (C4, arrowhead). On co-expressing EY and PB, ectopic eye formation was abolished (C7). Expression of the so-lacZ enhancer trap line was examined in eye antenna (C2,5,8) or wing discs (C3,6,9). ß-Galactosidase was induced by EY (C5,6 arrow) but not by PB (C2,3). Co-expression of PB with EY inhibits so activation in all tissues examined (C8,9, arrow).