Soluble frizzled-related proteins (sFRPS) function as modulators of Wnt signaling through direct interaction with Wnts. They have a role in regulating cell growth and differentiation in specific cell types (PubMed:27355534). SFRP4 plays a role in bone morphogenesis (PubMed:27355534). May also act as a regulator of adult uterine morphology and function. May also increase apoptosis during ovulation possibly through modulation of FZ1/FZ4/WNT4 signaling (By similarity). Has phosphaturic effects by specifically inhibiting sodium-dependent phosphate uptake (By similarity). Expressed in the ovary. Localized to granulosa cells of periovulatory follicles and corpora lutea. Weakly expressed in adult tissues including kidney, brain and lung. Only weakly expressed in developing embryo except for developing teeth, eye and salivary gland. In the developing eye, from 12.5 dpc, expressed in the future neural retina, in both the inner and outer cell layers. In the developing teeth, strong expression detected in the developing incisor teeth at 14.5 dpc. Expression localized to the mesenchyme of the dental follicle surrounding the enamel organ only at the early cap stage. Highly expressed in the branching epithelium of the salivary gland. Induced in ovaries by chorionic gonadotropin (CG). The FZ domain is involved in binding with Wnt ligands. Mice laking Sfrp4 have increased trabecular bone, reduced cortical-bone thickness, and failure of bone modeling during growth, resulting in wider bones with thinner and mechanically inadequate cortexes. Belongs to the secreted frizzled-related protein (sFRP) family.