The Fzd7/Wnt7a signal is strictly noncanonical. (A) Wnt3a induces a dose-dependent increase in TOP-flash luciferase reporter activity in C2C12 cells. Error bars represent means ± SEM; n = 3. *, P < 0.05. n.s., no significant difference. (B) Wnt7a does not activate the TOP-flash reporter at any tested concentration. Error bars represent means ± SEM; n = 3. (C) Wnt7a treatment decreases the abundance of peripheral Fzd7-YFP and leads to its accumulation in intracellular clusters (arrowheads). Bar, 5 µm. (D) Inhibition of clathrin-dependent endocytosis with monodansylcadaverine (MDC) prevents Wnt7a-induced migration of primary myoblasts in scratch assays. Error bars represent means ± SEM; n = 3. ***, P < 0.001. (E) Substantial amounts of Wnt7a-HA are present in intracellular stores (arrowhead) 72 h after a 3-h exposure to conditioned supernatants produced in COS-1 cells (top). In primary myoblasts from Fzd7^−/− mice, Wnt7a does not show such intracellular accumulation (bottom). Bars, 2 µm.