Ligand for members of the frizzled family of seven transmembrane receptors. Functions in the canonical Wnt/beta-catenin signaling pathway. Plays a redundant role in embryonic lung development. Forms a soluble 1:1 complex with AFM; this prevents oligomerization and is required for prolonged biological activity (PubMed:26902720). The complex with AFM may represent the physiological form in body fluids (PubMed:26902720). Interacts with FZD4 and FZD5 (By similarity). Isoform 1 is expressed in adult heart, brain, placenta, lung, prostate, testis, ovary, small intestine and colon. In the adult brain, it is mainly found in the caudate nucleus, subthalamic nucleus and thalamus. Also detected in fetal brain, lung and kidney. Isoform 2 is expressed in fetal brain, fetal lung, fetal kidney, caudate nucleus, testis and cancer cell lines. Palmitoleoylation is required for efficient binding to frizzled receptors. Depalmitoleoylation leads to Wnt signaling pathway inhibition. The disease is caused by variants affecting the gene represented in this entry. Belongs to the Wnt family.