The relative expression amounts of apterous and its co-factor dLdb/Chip are critical for dorso-ventral compartmentalization in the Drosophila wing

Dorso-ventral axis formation in the Drosophila wing requires the localized accumulation of the Apterous LIM/homeodomain protein (Ap) in dorsal cells. Here we report that dLdb/Chip encodes a LIM-binding cofactor that controls Ap activity. Both lack and excess of dLdb/Chip function cause the same phen otype as apterous tap) lack of function; i.e. dorsal to ventral transformat ions, generation of new wing margins, and wing outgrowths. These results in dicate that the normal function of Ap in dorso-ventral compartmentalization requires the correct amount of the DLDB/CHIP cofactor, and suggest that th e Ap and DLDB/CHIP proteins form a multimeric functional complex, In suppor t of this model, we show that the dLdb/Chip excess-of-function phenotypes c an be rescued by ap overexpression.