A.m.H recruits Drosophila co-repressorsand downregulates transcription of the Notch target gene vestigial. A) Wild type and mutant A.m.H constructs that are deficient in binding Gro, CtBP or both as schematically depicted, were overexpressed in the central wing blade using the omb-Gal4 driver line. Overexpression of these constructs results in deep wing incisions, ranging from nearly complete loss of the wing blade to large notches. Note shortening of longitudinals L4 and L5 upon overexpression of UAS-AmHGC* which cannot recruit any co-repressor (arrowheads). Control flies are omb-Gal4 × UAS-lacZ. Wings are from female flies reared in parallel at 25°C. B) Wild type and mutant A.m.H constructs as depicted above were overexpressed in the central wing domain with omb-Gal4 at 25°C. Expression of the vgBE-lacZ reporter gene was determined by anti-beta-galactosidase staining (green). The control disc (omb-Gal4; vgBE-lacZ) shows the typical expression in a thin strip of cells along the dorso-ventral boundary (green). Ectopic expression of A.m.H (red nuclear staining) completely represses vg-transcription (arrowhead) within the A.m.H overexpression domain (outlined with yellow dots). Lack of Gro co-repressor binding (AmHG*) interferes only little with vg-repression, whereas CtBP is clearly more important for H repressor activity (AmHC* and AmHGC*). Expression of A.m.H protein was monitored with antisera (red nuclear staining). Note disturbed wing disc morphology of omb-Gal4>UAS-AmH animals (arrow).