Fig. 4. The roles of Wg receptors in extracellular Wg distribution. Extracellular Wg staining in wing discs carrying mutant clones for fz (A,A'), fz2 (B,B'), fz-fz2 (C,C') and arr (D,D'). Discs are oriented dorsal top-right, anterior top-left (A-B'), and dorsal right, anterior up (C-D'). The mutant clones are marked by the absence of GFP and outlined by broken lines, except in D. Extracellular Wg is not altered in mutant clones for fz or fz2 alone. By contrast, it is increased in clones mutant for fz-fz2 and arr. The yellow arrows indicate the presumptive ectopic Wg-expressing cells, and the blue arrows indicate the mutant cells accumulating Wg on the cell surface (C,D).