Fig. 7. Expression of Hh-N in peripodial cells induces broad activation of dpp expression. dpp-lacZ (red) expression in wing imaginal discs with clones (marked by GFP in green) of cells expressing Hh-Np (A,B), both Hh-Np and Disp (C), Hh-N (D-F) or Hh-CD2 (G,H) produced using the FRT flip-out technique. (B,E,H) Confocal z-sections (apical side upwards) made at the level indicated by the white lines in A,D,G, respectively. Peripodial clones expressing the different Hh forms are delimited by broken lines (A,D,G). (I) enGal4 UAS-GFPnuc imaginal wing disc. Peripodial clones expressing Hh-Np (A,B) or Hh-CD2 (G,H) do not trigger outgrowth of the discs, and induce dpp only in underlying columnar cells when the clones are located above the hinge region of the disc proper. By contrast, Hh-N clones in the peripodial membrane induce anterior compartment outgrowth and broad (in 40% of the observed discs, as in D) or moderate (in 60% of the observed discs, as in F) dpp expression in the disc proper in both the wing pouch and the hinge regions, although not in the notum region (D-F). Peripodial clones expressing both Hh-Np and Disp induce disc outgrowth with a moderate level of dpp expression in the disc proper (C). In enGal4 UAS-GFP discs, all the P cells and the first two rows of A cells of the disc proper are fluorescent (I) (the AP border is delimited by the double-headed arrow, based on the lower fluorescent signal observed in A cells). The large GFP-positive nuclei located in the upper layer correspond to the peripodial membrane (arrows in I). GFP-positive peripodial cells are above the A cells of the disc proper. (J,K) Schemes and model summarising the various data obtained for Hh-Np and Hh-N, respectively. Clones of Hh-Np expression in the disc proper induce widespread dpp expression, whereas similar Hh-N clones induce only narrow domains of dpp expression. In the disc proper, Hh-Np is enriched apically (ap), whereas Hh-N is enriched at the basolateral (bl) membrane. By contrast, clones of Hh-N in the peripodial membrane (PM) allow luminal diffusion of Hh-N, inducing widespread dpp expression in the wing pouch and the hinge. Peripodial Hh-Np clones induce dpp in the hinge through cellular interactions, with no apparent consequences for the wing pouch. When both Disp and Hh-Np are present in peripodial cells, luminal secretion of Hh-Np is permitted, resulting in outgrowth and moderate levels of dpp expression in the wing pouch (hatched area). n, notum; h, hinge; wp, wing pouch.