The frizzled gene was originally identified in Drosophila melanogaster and was shown to be involved in the development of tissue polarity. The mammalian homolog of frizzled, as well as several mammalian frizzled-related proteins, FRP-1 (also designated SARP2), FRP-2 (also designated SARP1), FRP-3 and SARP3 (also designated FRP-5) have been identified. Frizzled is a transmem- brane protein that functions as a receptor for Wnt. The frizzled related proteins FRP-1, FRP-2, FRP-3 and SARP3 are secreted proteins that contain regions of homology to the cysteine-rich ligand-binding domain of frizzled. The FRPs/ SARPs have also been shown to be involved in the Wnt signaling pathway by regulating the intracellular levels of β-catenin.
