Fig. 4. cmn acts upstream of ptc. (A) Wild-type wing disc, (B) cmn homozygous wing disc and (C,D) cmn homozygous wing disc carrying a clone of ptc mutant cells, were stained to show dpp-lacZ reporter expression (red) and a marker gene (Myc) expression (green in D). ptc mutant cells are recognized by the lack of Myc expression. The cmn mutant disc exhibits diminished levels of dpp-lacZ expression (arrowhead in B). In contrast, cmn ptc double mutant cells situated in the anterior compartment express wild-type levels of dpp-lacZ (arrow in C and D) Arrowhead in C and D indicates dpp-lacZ expression at the AP boundary.