Ligand for members of the frizzled family of seven transmembrane receptors (PubMed:12490564). Functions in the canonical Wnt/beta-catenin signaling pathway (PubMed:12490564). Acts as an upstream regulator of FGF10 in the lateral plate mesoderm during limb initiation in the embryo (PubMed:11290326). Interacts with FZD4 and FZD5. Detected at the marginal tip of the developing retina (PubMed:12490564). Expressed in the intermediate and the lateral plate mesoderm in the presumptive chick forelimb region. Expressed in the eye, head ectoderm, prospective forelimb mesenchyme, lung bud, pharyngeal arches, the brain and otic vesicle. At stage 11, expressed in the medial sites of the embryonic right and left coelom, as well as in the medial region of the forming somites. Between stages 14 and 16, expression in the presumptive wing field, with strongest expression at stage 15. At stage 17, a faint expression is detected in the posterior region of the nascent limb bud. Expressed in the ocular surface ectoderm, including the corneal epithelium, starting from the onset of the lens vesicle closing at stage 16. Palmitoleoylation is required for efficient binding to frizzled receptors. Depalmitoleoylation leads to Wnt signaling pathway inhibition. Belongs to the Wnt family. Was initially thought to be WNT13.