GROUCHO AND HEDGEHOG REGULATE ENGRAILED EXPRESSION IN THE ANTERIOR COMPARTMENT OF THE DROSOPHILA WING

Drosophila imaginal discs are divided into units called compartments, Cells belonging to the same compartment are related by lineage and exp ress a characteristic set of 'selector genes', The borders between com partments act as organizing centres that influence cell growth within compartments. Thus, in the cells immediately anterior to the anterior- posterior compartment boundary the presence of the hedgehog product ca uses expression of decapentaplegic, which, in turn, influences the gro wth and patterning of the wing disc. The normal growth of the disc req uires that posterior-specific genes, such as hedgehog and engrailed ar e not expressed in cells of the anterior compartment. Here we show tha t hedgehog can activate engrailed in the anterior compartment and that both hedgehog and engrailed are specifically repressed in anterior ce lls by the activity of the neurogenic gene groucho. In groucho mutant discs, hedgehog and engrailed are expressed at the dorsoventral bounda ry of the anterior compartment, leading to the ectopic activation of d ecapentaplegic and patched and to a localised increase in cell growth associated with pattern duplications, The presence of engrailed in the anterior compartment causes the transformation of anterior into poste rior structures.