Fig. 3. Pygo is required for Wg signaling in imaginal disc development. In these images, anterior is towards the left, dorsal is upwards. All the discs were derived from third instar larvae. Somatic clones mutant for pygo^F15 are marked by the absence of GFP shown in green. A complex pattern of Achaete (Ac) expression is shown in a wing disc from a wild-type third instar larva (A). Wg acts at short range to induce the expression of Ac at the DV boundary of anterior wing pouch (A). In a mosaic clone mutant for pygo^F15, which is marked by absence of GFP, the expression of Ac protein is abolished (B,B'). Note that a patch of Ac-positive cells within the clone is Wg independent. Therefore the expression of Ac in these cells is not diminished. In response to Wg signaling, Dll is expressed in a graded manner with highest expression in DV boundary in a wild-type wing disc (C). Dll expression is diminished autonomously in a pygo^F15 mosaic clone (D,D'). In a wild-type leg disc, Dpp-lacZ expression is repressed by Wg signaling in the ventral anterior quadrant (E). In a pygo^F15 mosaic clone of the leg disc, Dpp-lacZ expression is de-repressed (F,F'). In a wild-type wing disc, Dpp-lacZ expression is induced by Hh signaling at the AP boundary. The expression of Dpp-lacZ is not altered in mosaic clones mutant for pygo^F15 (H,H').