RSPO1 (R-spondin 1) is a member of the R-spondin family, a 28.9 kDa secreted activator protein. It has two cystein-rich, furin-like domains and one thrombospondin type 1 domain. In mice, the protein induces the rapid onset of crypt cell proliferation and increases intestinal epithelial healing,Porcineroviding a protective effect against chemotherapy-induced adverse effects.It is activator of the beta-catenin signaling cascade, leading to TCF-dependent gene activation. Acts both in the canonical Wnt/beta-catenin-dependent pathway,Porcineossibly via a direct interaction with Wnt proteins, and in a Wnt-independent beta catenin pathway through a receptor signaling pathway that may not use frizzled/LRP receptors. Acts as a ligand for frizzled FZD8 and LRP6. May negatively regulate the TGF-beta pathway. Has a essential roles in ovary determination.