Fig. 6. Dally-like is required upstream or at the level of Patched in the Hedgehog pathway. (A-C) Assays for the range of Hh signalling. (A) ArmGal4VP16/UASdlp embryos ubiquitously express Dlp at high levels, but wg transcription is activated in a single row of cells, as in wild type, showing that Dlp does not stimulate the range of Hh signalling in embryos. (B) In contrast, increasing the concentration of wild-type Hh in the cells that normally secrete it (the En cells) stimulates wg transcription over two to three cell diameters. (C) Repeating the same experiment with Hh-N leads to the stimulation of wg transcription over three to five cell diameters. (D-F) Epistatic relationship between patched (ptc) and dlp. (D) In ptc homozygous null mutant embryos, Hh signalling is constitutively activated and as a result wg transcription is stimulated in the whole competence domain. (E) In ptc^- homozygous embryos injected for dlp dsRNA, ectopic wg transcription is unaffected showing that Dlp is not required for the constitutive activation of Hh signalling. (F) In sibling embryos which are heterozygous for ptc and thus wild type for Hh signalling, dlp RNAi leads to the disappearance of endogenous wg as expected. ptc heterozygous and homozygous embryos were separated in this experiment by the presence of lacZ expression in the heterozygous embryos (signal at the midline in F).