DER signaling restricts the boundaries of the wing field during Drosophiladevelopment

Arthropod and vertebrate limbs develop from secondary embryonic fields. In insects, the wing imaginal disk is subdivided early in development into the wing and notum subfields. The activity of the Wingless protein is fundamen tal for this subdivision and seems to be the first element of the hierarchy of regulatory genes promoting wing formation. Drosophila epidermal growth factor receptor (DER) signaling has many functions in fly development. Here we show that antagonizing DER signaling during the second larval instar le ads to notum to wing transformations and wing mirror-image duplications. DE R signaling is necessary for confining the wing subregion in the developing wing disk and for the specification of posterior identity. To do so, DER s ignaling acts by restricting the expression of Wingless to the dorsal-poste rior quadrant of wing discs, suppressing wing-organizing activities. and by cooperating in the maintenance of Engrailed expression in posterior compar tment cells.