Ligand for members of the frizzled family of seven transmembrane receptors that functions in the canonical Wnt/beta-catenin signaling pathway (By similarity). Plays an important role in embryonic development, including dorsal versus ventral patterning during limb development, skeleton development and urogenital tract development. Required for central nervous system (CNS) angiogenesis and blood-brain barrier regulation (By similarity). Forms a soluble 1:1 complex with AFM; this prevents oligomerization and is required for prolonged biological activity. The complex with AFM may represent the physiological form in body fluids (By similarity). Interacts with FZD5. Interacts with PORCN (By similarity). Palmitoleoylation is required for efficient binding to frizzled receptors. Depalmitoleoylation leads to Wnt signaling pathway inhibition. Belongs to the Wnt family.