SHAGGY AND DISHEVELLED EXERT OPPOSITE EFFECTS ON WINGLESS AND DECAPENTAPLEGIC EXPRESSION AND ON POSITIONAL IDENTITY IN IMAGINAL DISCS

The finding that Wingless (WG) and Decapentaplegic (DPP) suppress each others transcription provides a mechanism for creating developmental territories in fields of cells. Here, we address the mechanism of that antagonism. The dishevelled (dsh) and shaggy (sgg) genes encode intra cellular proteins generally thought of as downstream of WG signaling. We have investigated the effects of changing either DSH or SGG activit y on both cell fate and wg and dpp expression. At the level of cell fa te in discs, DSH antagonizes SGG activity. At the level of gene expres sion, SGG positively regulates dpp expression and negatively regulates log expression while DSH activity suppresses dpp expression and promo tes wg expression. Sharp borders of gene expression correlating precis ely with clone boundaries suggest that the effects of DSH and SGG on t ranscription of wg and dpp are not mediated by secreted factors but ra ther act through intracellular effecters. The interactions described h ere suggest a model for the antagonism between WG and DPP that is medi ated via SGG. The model incorporates autoactivation and lateral inhibi tion, which are properties required for the production of stable patte rns. The regulatory interactions described exhibit extensive ability t o organize new pattern in response to manipulation or injury.