Ligand for members of the frizzled family of seven transmembrane receptors (Probable). Plays an important role in the embryonic development of the urogenital tract and the lung (PubMed:7990960, PubMed:9989404, PubMed:16054034, PubMed:17537789, PubMed:19830824, PubMed:26321050). Required for normal mesenchyme to epithelium transition during embryonic kidney development (PubMed:7990960, PubMed:16054034, PubMed:17537789, PubMed:19830824). Required for the formation of early epithelial renal vesicles during kidney development (PubMed:16054034). Required for normal formation of the Mullerian duct in females, and normal levels of oocytes in the ovaries (PubMed:9989404, PubMed:19830824). Required for normal down-regulation of 3 beta-hydroxysteroid dehydrogenase in the ovary (PubMed:9989404). Required for normal lung development and for normal patterning of trachael cartilage rings (PubMed:26321050). Interacts with PORCN (PubMed:10866835). Interacts with PKD1 (By similarity). In adults in lung and brain. Detected along the length of the mesonephros at 9.5 to 10.5 dpc. At 11.0 dpc, detected in the mesenchyme of the gonads in both sexes and in mesonephros. At 11.5 dpc, sex-specific differentiation of the gonads begins, and Wnt4 is down-regulated in male gonads, but not in female gonads. Detected in mesenchyme cells underlying the newly formed Mullerian duct in females, but not in the Wolffian duct in males (PubMed:9989404). During kidney development, detected at 11.5 dpc in condensed mesenchymal cells on both sides of the stalk of the ureter. Detected on pretubular aggregates upon initiation of ureteric bud branching at 12.5 dpc. Detected on primitive tubular aggregates at 13.5 dpc. Detected on comma-shaped and S-shaped bodies by 14.5 dpc, and is restricted to kidney cortex by 16.5 dpc (PubMed:7990960). Palmitoleoylation is required for efficient binding to frizzled receptors. Depalmitoleoylation leads to Wnt signaling pathway inhibition. Mutant embryos show normal early stages of kidney development, but later stages of kidney development are disrupted (PubMed:7990960, PubMed:19830824). Mutant embryos develop to term, but the pups die within 24 hours after birth, probably due to the absence of functional kidneys (PubMed:7990960). Reproductive organs in newborn males appear normal (PubMed:9989404). External genitalia from newborn females appear normal, but they lack a Mullerian duct and their gonads and sex ducts appear masculinized (PubMed:9989404, PubMed:19830824). Their ovaries contain less than 10% of the normal number of oocytes, and these are in the process of degenerating (PubMed:9989404). Mutant embryos display altered patterning of tracheal cartilage rings. By 13.5 dpc the size of their lungs is significantly reduced, and at 17.5 dpc the left lung lobe is on average 35% smaller than for wild-type (PubMed:26321050). Belongs to the Wnt family.