Fig. 4. The degrading activity of Arrow is specific to Frizzled2. (A,A') Wingless stabilized by Dally-like, as shown in A, is only weakly reduced by further addition of Arrow, as shown in A'. (B-B') Likewise, Arrow does not degrade Wingless stabilized by Frizzled2GPI. (C-C') Expression of a form of Frizzled2 that lacks most of the intracellular tail (Frizzled2C) causes Wingless accumulation at the cell surface (C, main panel) and appears to reduce Wingless internalization (as seen at high magnification in the inset; compare with Fig. 2A'). As shown in C', such accumulation is abrogated by Arrow overexpression. This result provides indirect evidence that Arrow contains an endocytic (in addition to a degradation) signal as it can promote the removal of Frizzled2C-complexed Wingless from the cell surface. (D,D') A form of Arrow that lacks amino acids 1477 to 1612 (ArrC) is deficient in degradation activity. This is shown in an imaginal disc expressing ArrC in the posterior compartment. A pulse of Frizzled2 expression (from hs-Frizzled2) was induced 1.5 hours prior to fixation. (D) ArrC expression detected with anti-HA; (D') the distribution of Wingless. Double-headed arrows mark the extent of the Wingless range in the two halves of the disc. In the posterior compartment, the domain where Wingless vesicles are detected is expanded.