Figure 2. Hh^C85S expressed in the posterior wing disc compartment, but not in the anterior compartment, dominantly represses the formation of Hh-dependent wing structures (a) Drosophila third-instar wing disc and adult wing.

An en >GFP control wing disc and wing are shown. The posterior en-expression domain of the wing disc is labeled in green. Adult wings are shown with anterior up and proximal left. Longitudinal veins L1-L5, the anterior cross vein (acv) and the posterior cross vein (pcv) are marked. The anterior (a)/posterior (p) compartment border is shown as a red dashed line. (b) Schematic of transgenic constructs. P: palmitate, C: cholesterol, CW: Cardin-Weintraub motif. (c) Hh overexpression under en-control (en >Hh) expands the anterior L3-L4 intervein region. (d) en >Hh^C85S: L3 and L4 appose proximally; the acv is lost. (e,f) To quantify Hh activity, the most proximal L3-L4 areas highlighted in orange were determined and the values obtained divided by the L2-L3 areas. ***p≤0.001, **p≤0.01, n = 20. (g,h) Ptc-controlled GFP and Hh^C85S expression in the anterior (Hh-receiving) wing disc compartment at the a/p border (red stripe) do not impair wing development. (i) Left: Proposed mixed composition of morphogen clusters upon transgenic Hh^C85S (gray) expression in the posterior compartment that simultaneously produces the wild-type morphogen (green). Here, the N-terminal peptide of one molecule in the chain blocks the Ptc-receptor-binding site (red) of the adjacent molecule in the chain. Shh crystal lattice interactions (pdb: 3m1n) are shown to illustrate a possible cluster structure. Right: Hh^C85S expression in the anterior compartment (under ptc control) prevents the assembly of mixed morphogen clusters, leaving endogenous Hh function unimpaired.