Fig. 6. Wingless accelerates Frizzled2 internalization. (A,B) Imaginal disc of the genotype hs-FLAG-Frizzled2 fixed 1.5 hours after a pulse of uniform expression of tagged Frizzled2 (A) and Wingless (B). Note the relative increase in vesicular Frizzled2 around the area of Wingless expression. As many of these vesicles also contain Wingless (insets), it appears that Wingless stimulates Frizzled2 internalization. (C,D) Imaginal discs of the same genotype (hs-FLAG-Frizzled2) fixed 50 minutes (C) or 3 hours (D) after heat-shock and stained with anti-FLAG. Fifty minutes after the pulse, Frizzled2 is found throughout the disc, predominantly outlining cell membranes, whereas after 3 hours, the level of Frizzled2 appears preferentially reduced in the area surrounding the source of Wingless (the central region of the pouch) suggesting, possibly, increased degradation. (E) Imaginal disc 1 hour after uniform induction of Patched expression. The protein (as detected with an anti-Patched antibody) is seen uniformly throughout the disc. (F) Three hours after induction, the Patched protein is preferentially reduced in the posterior compartment, where its ligand, Hedgehog is expressed. Staining along the anteroposterior boundary could originate from endogenous expression as an anti-Patched antibody was used. However, deeper into the anterior and posterior compartments, Patched is not normally expressed and protein turnover can be compared in these two domains. (G,H) Division of labour between Frizzled2 and Arrow. (G) Frizzled2 provides most of the capturing activity, while Arrow brings a degradation signal. Both receptors provide an internalization signal. (H) When Frizzled2 is in relative excess at the cell surface, Wingless is captured and put on hold until Arrow becomes available to signal and trigger degradation.