Fig. 7. Continuous requirement of engrailed and hedgehog in groove formation. When driven by paired-gal4, expression of engrailed and hedgehog rescues segmental grooves only transiently (in an embryo lacking engrailed and also wingless). (A) Side view of such an embryo at stage 12, focused on the ventral midline. Shallow grooves can be seen (arrows). (B) At stage 13, these grooves are no longer visible. (C) Schematic representation of the domains of paired (Prd) and buttonhead (Btd) expression. Note that, in the ventral region, expression of buttonhead persists longer (up to stage 15) than that of paired (to stage 12+). (D) buttonhead-driven engrailed expression rescues groove formation (arrows) in an engrailed mutant even at stage 13 and beyond. This is not true of paired-gal4-driven engrailed (not shown).

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