THE FUNCTION OF ENGRAILED AND THE SPECIFICATION OF DROSOPHILA WING PATTERN

The adult Drosophila wing (as the other appendages) is subdivided into anterior and posterior compartments that exhibit characteristic patte rns. The engrailed (en) gene has been proposed to be paramount in the specification of the posterior compartment identity, Here, we explore the adult en function by targeting its expression in different regions of the wing disc, In the anterior compartment, ectopic en expression gives rise to the substitution of anterior structures by posterior one s, thus demonstrating its role in specification of posterior patterns, The en-expressing cells in the anterior compartment also induce:high levels of the hedgehog (hh) and decapentaplegic (dpp) gene products, w hich results in local duplications of anterior patterns. Besides, hh i s able to activate en and the engrailed-related gene invected (inv) in this compartment, In the posterior compartment we find that elevated levels of en product result in partial inactivation of the endogenous en and inv genes, indicating the existence of a negative autoregulator y mechanism, We propose that en has a dual role: a general one for pat terning of the appendage, achieved through the activation of secreted proteins like hh and dpp, and a more specific one, determining posteri or identity, in which the inv gene may be implicated.