Fig. 6. Hedgehog-independent requirement of Engrailed in groove formation. Engrailed is required in addition to Hedgehog for boundary formation. No grooves form in an engrailed mutant (or in an engrailed wingless double mutant). (A) Groove formation is rescued, at least in the lateral epidermis (see legend of Fig. 7), by expressing engrailed with paired-gal4, shown here in the wingless engrailed double mutant: grooves form on both sides (arrows) of the expression domain because of the absence of wingless. (B) By contrast, no such rescue is seen when Hedgehog is expressed in the same genetic background. (C,D) Diagrams summarising the results in A and B. (E) Stage 13 embryo expressing CiVP16 under the control of engrailed-Gal4 stained with anti-Engrailed (brown) and a ci RNA probe (purple). This embryo is expected to have active Hedgehog signalling on both sides of the presumptive boundaries. Boundary formation is not prevented. This is represented diagrammatically in F.