Fig. 8. Hh requires HSPGs in order to move. (A,D,G) Hh distribution; (B,E,H) merged images of Hh distribution (purple), with cells of the imaginal disc marked uniformly with GFP (green). The clone of cells mutant for EXT originated from a single cell lacking EXT activity, created by mitotic recombination and marked by the absence of GFP. Thus, cells homozygous for the EXT mutant are marked by an absence of GFP and cells heterozygous for the EXT mutant are pale green. The staining intensity of Hh in the selected area (white boxes in B and E) was integrated along AP axis, plotted using NIH Image software and presented schematically (C,F). (A-C) Hh protein synthesized in the posterior compartment appears to flow into the anterior compartment, with a moderate concentration gradient starting from the middle of the posterior compartment. (D-F) Hh accumulates abnormally in the posterior compartment when the EXT mutant clone is in the anterior compartment along the AP boundary. The A/P boundary is depicted with blue lines (A,D). (G,H) When the EXT mutant clone is produced in the posterior compartment, Hh accumulation is reduced.