Fig. 5. Different levels of Wg signaling activate Dll and dac. (A) Expression of Dll (green), dac (blue) and brk (red) in a wild-type third instar leg disc. The individual channels are shown below. (A') Expression of Dll (green) and Dac (blue) in a wild-type third instar leg disc. (B-B''') In wg^CX4/CX3 discs, the Dll (green) domain is reduced in size compared with wild type (compare with A) and the Dac (blue) domain is expanded ventrally (arrow). brk is repressed in the ventral domain because of dpp derepression (data not shown). (C-C''') In brk^XA;wg^CX4/CX3 discs, the Dll domain is reduced in size compared with wild type and the Dac domain is nearly circular. Compare discs in B and C with a wild-type disc in A and A'. The Dll-only domains in leg discs of this genotype and in wg^CX4/CX3 discs vary from small (as in the example in B) to its complete absence (as in the example in C). (D-E'') brk^-; tub>axin+ clones marked positively by lacZ (green) grown at different temperatures. (D) At 25°C, axin levels are sufficient to block both Dll and dac derepression (arrow). Compare with the brk^- clone in Fig. 2B, showing both Dll and dac derepression. (D'') Cross-section of the same disc as in D showing the location of the clone (broken line, arrow). (E) Leg disc of the same genotype in D grown at 17°C. The Wg signaling that remains permits dac but not Dll derepression (arrow). Approximately one-third of these clones show dac only derepression like the clone shown here, a phenotype that is never observed in brk^- clones. Approximately two thirds of these clones show derepression of both genes similar to the clone shown in Fig. 2B. (E'') Cross-section of the same disc in E showing the location of the clone (broken line, arrow).