Fig. 5. Wingless signalling inhibits segmental boundary formation. All embryos are at stage 13+ and stained by immunocytochemistry with anti-Engrailed (black). (A-D) Removal of Wingless (while maintaining engrailed expression) leads to duplication of segment boundaries. An `en face' view of the ventral area (A) shows that engrailed stripes are sharply delineated on both sides. In a side view of the ventral region (B), one can see grooves on both sides of engrailed stripe (e.g. black arrows). In the lateral region, an `en face' view (C) shows that Engrailed stripes are broken up into clumps. (D) Grooves are generated around the islands of engrailed-positive cells as seen in a side view. (E-G) In a double mutant (wingless^– hedgehog^–), no groove forms. (E) Engrailed stripes are disrupted throughout (en face view of the ventral region as in A). (F) Ventral grooves are no longer generated, as seen in a side view as in B. (G) Likewise no groove can be recognised laterally in a side view similar to that in D. (H,I) Schematic drawings summarising the results shown in A-G.

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