DISTINGUISHABLE FUNCTIONS FOR ENGRAILED AND INVECTED IN ANTERIOR-POSTERIOR PATTERNING IN THE DROSOPHILA WING

SUBDIVISION Of the limb primordia into compartments initiates pattern formation in the developing limbs(1,2). Interaction between distinctly specific cells in adjacent compartments leads to localized expression of the secreted signalling molecules Wingless (Wg) or Decapentaplegic (Dpp) which in turn organize pattern and control growth of the limbs The homeobox gene engrailed has been implicated in specification of po sterior cell fate(9-12), whereas the LIM/homeobox gene, apterous, spec ifies dorsal fate(3). Removing apterous activity causes a complete tra nsformation from dorsal to ventral fate and leads to the formation of an ectopic dorsal-ventral boundary organizer(3,13). By contrast, remov ing engrailed activity causes incomplete morphological transformation from posterior to anterior fate in the wing(10,14,15), and fails to pr oduce an ectopic anterior-posterior organizer (reviewed in ref, 2). Co mplete transformation can only be effected by simultaneously eliminati ng activity of engrailed and its homologue invected(16-18). Here we sh ow that invected functions principally to specify posterior cell fate. Thus establishment of the anterior-posterior organizer and control of compartment identity are genetically distinguishable, and invected ma y perform a discrete subset of functions previously ascribed to engrai led.