Fig. 3. Hh-dependent gene expression along the AP boundary. (A) Anterior cells are marked by the expression of ci, shown in red. Posterior cells are marked by anti-En/Inv staining shown in blue. A broken line marks the approximate position of the AP boundary. en is required in posterior cells for hh expression; hh^Gal4 UAS-GFP is shown in green. Anterior cells adjacent to the AP boundary respond to Hh by activating target gene expression. A narrow, Hh-dependent stripe of anti-En/Inv staining can be detected in anterior cells by late third instar (purple). The expression of two additional Hh target genes can be detected in anterior cells; (B) ptc-lacZ, is shown in blue and (C) dpp-lacZ, is shown in yellow. Brackets highlight the domains of anterior Hh target gene expression.