Ligand for members of the frizzled family of seven transmembrane receptors. Probable developmental protein. Palmitoleoylated by porcupine. The lipid group functions as a sorting signal, targeting the ligand to polarized vesicles that transport WNT-1 to unique sites at the cell surface. Depalmitoleoylated by notum, leading to inhibit Wnt signaling pathway. Belongs to the Wnt family.