DECAPENTAPLEGIC OVEREXPRESSION AFFECTS DROSOPHILA WING AND LEG IMAGINAL DISC DEVELOPMENT AND WINGLESS EXPRESSION

We have used the GAL4-UAS expression system to increase the level of e xpression of the Drosophila gene decapentaplegic (dpp) in a pattern ap proximating its normal pattern in leg and wing imaginal discs. Interme diate increases-of dpp expression have little effect in wing discs but high levels of dpp overexpression lead to reduction of the scutellum and duplication of posterior wing structures. In leg discs intermediat e increases cause supernumerary outgrowths of ventral leg structures i n the anterior-ventral region. Greater increases of dpp expression cau se the loss of ventral leg structures with the concomitant fusion of l eft and right dorsal forelegs. The defects observed in both legs and w ings appear to arise through dose-dependent effects of dpp on wingless (wg) expression. A high level of dpp overexpression in the wing disc causes reduction of wg expression in the presumptive scutellar region, consistent with the subsequent reduction of the scutellum. An interme diate increase of dpp expression in leg discs induces the expansion of wg expression into the ventral outgrowths. At higher dpp expression l evels, ventral wg expression in leg discs is eliminated, consistent wi th the loss of ventral leg cuticle. In the leg disc end knob and in th e wing margin primordium, where wg and dpp cooperate in producing dist al outgrowth, dpp overexpression has no detectable effect either on pa tterning or on wg expression. We propose that a critical role for dpp in other regions of the leg and wing discs is to reduce or block the e xpression of wg. This role of dpp is supported by the observation that ectopic wg expression is detected in imaginal discs where dpp signali ng is compromised by lowering the activity of one of its receptors, tk v. This antagonism between dpp and wg expression may be critical to as signing only one disc region as the distal organizer. (C) 1996 Academi c Press, Inc.