RSPO1 (R-spondin 1) is a secreted protein that functions as a potent activator of the canonical Wnt signaling pathway through multiple mechanisms. RSPO1 acts as a ligand for LGR4-6 receptors, which upon binding associate with phosphorylated LRP6 and frizzled receptors to trigger canonical Wnt signaling 1. Additionally, RSPO1 functions as a direct antagonist of RNF43 and ZNRF3 transmembrane ligases, preventing these negative regulators from suppressing Wnt signaling 1. In intestinal stem cell biology, RSPO1 works cooperatively but non-interchangeably with Wnt ligands - while Wnt proteins maintain RSPO receptor expression and provide basal competency, RSPO1 actively drives stem cell self-renewal and expansion 2. RSPO1 plays essential roles in ovarian determination and development through the WNT/β-catenin pathway 3. Clinically, RSPO1 mutations are associated with keratoderma and sex reversal. Recent studies have also implicated RSPO1 in metabolic regulation, where gain-of-function mutations suppress beige adipocyte thermogenesis and contribute to diet-induced obesity through LGR4-Wnt/β-catenin signaling 4. RSPO1 has therapeutic potential for tissue regeneration, as dual WNT3A/RSPO1 treatment can promote liver repair and organoid growth 5.