Fig. 4. Regulation of Scr by Pb. (A-C) Expression of Dll (green), Dac (red) and Scr (blue) in a pb5 labial disc. (B) The Dac (red) expression domain completely overlaps the expression domain of Dll (green). (C) Scr (blue) and Dac (red) expression in a pb5 labial disc. Note the gap in Scr accumulation that coincides with the band of Dac-positive cells and that there is no detectable Scr accumulation in the distal end of the disc. For comparison with wild-type Scr expression in the labial disc, refer to Fig. 5A. (D-F) Same disc showing individual channels of Dll, Dac and Scr. (G) Wild-type T3 leg disc stained with anti-Scr (green) and anti-Dac (red) antibodies. There is no overlap (yellow) of accumulation. (H) The Dac (red) ring is interrupted by the Scr (green) -expressing cells in a dpp=>pb T3 leg disc. No overlap (yellow) between Dac and Scr is detected. (I) Ectopic expression of Scr (green) in a dpp=>pb wing disc. Again there is no co-expression of Scr and Dac. W, wing disc.