Fig. 4. Dll and dac expression in the absence of Dpp signaling and brk. (A-A'') Mitotic clones mutant for brk (arrow; marked by the absence of GFP, green, and outlined in red in A'') and tkv [arrow; marked by the absence of arm-lacZ (red) and outlined in yellow in A''] derepress Dll. These clones were induced separately and therefore result in independent clonal events. Cells mutant for both genes show no GFP (green) and no β-gal staining (red) (A'). (A'') Dll is derepressed cell autonomously throughout the brk^- clone (marked by the red line), including cells that are also tkv^- (marked by the yellow line). (B-B'') Cross-section of the same disc in A showing that the brk^-; tkv^- clone is proximal to the Dll expression domain (arrow, outlined in yellow). (B'') Schematic representation of the cross-section shown in B. Dll expression is shown in gray and the yellow arrow marks the region where Dll is derepressed (dark gray). tr, trocanter. (C-C'') A proximal clone doubly mutant for brk (absence of GFP, green) and tkv (absence of arm-lacZ, green) showing derepression of Dll (arrowhead, red) and dac (arrow, blue). These clones were induced at the same time, and are therefore congruent. (D-D') Cross-section of the same disc as in C showing that the brk^-;tkv^- clone (outlined in yellow) is proximal to the Dll and dac expression domains.