Fig. 2. Engrailed and rhomboid expression in dally-like RNAi embryos. (A-D) Antibody staining against En in stage 11 embryos. Wild-type En expression (A). En expression in the ectoderm is completely gone in a wg null mutant (B), and has just started to fade in a hh null mutant (C) and dlp RNAi embryos (D). (E) Schema representing the autoregulatory loop between wg, en and hh at stage 9-10 in the ectoderm. As a consequence of this loop, En is lost earlier in wg mutants than in hh mutants. Note that at this stage, the gradient of Wg protein is symmetrical. PS: parasegment boundary. (F-I) Antibody staining against En in stage 12 embryos. En expression is mostly gone in a hh null mutant (H) and dlp RNAi embryos (I). Mutant phenotypes were found in dlp RNAi embryos in 87% of cases (n=140). (J) Schema showing the segmental gene regulation at stage 11-12. At stage 11, En expression becomes independent of Wg, and the Wg gradient becomes asymmetrical. The parasegment groove (PS) disappears around stage 12 when the segment boundary (S) groove starts to be visible. (K-N) In situ hybridisation against rhomboid (rho) in stage 14 embryos. In wild type, rho is expressed in one stripe per segment (K), whereas two stripes per segment are found in the wg null mutant (L). In dlp RNAi embryos (75%, n=24) (N), as in a hh null mutant (M), one irregular stripe is found per segment as in wild type, suggesting that loss of dlp mimics the loss of hh. (O) Schema depicting the intrasegmental patterning occurring in stage 12-14 embryos. Wg represses rho expression on the anterior side of the Engrailed domain, whereas hh and serrate (ser) maintain rho expression on the posterior side. S, segment boundary.