Ligand for members of the frizzled family of seven transmembrane receptors that functions in the canonical Wnt/beta-catenin signaling pathway. 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. Required for normal, sexually dimorphic development of the Mullerian ducts, and for normal fertility in both sexes. Required for normal neural stem cell proliferation in the hippocampus dentate gyrus. Required for normal progress through the cell cycle in neural progenitor cells, for self-renewal of neural stem cells, and for normal neuronal differentiation and maturation. Promotes formation of synapses via its interaction with FZD5 