R-Spondin 3 Proteins and Enzymes

R-Spondin 3 (RSPO3; Cristin 1) is a secreted Wnt regulating protein that is critical for development of the placental labyrinthine layer. It is expressed in the roof plate, tail, somites, otic vesicles, cephalic mesoderm, truncus arteriosus, atrioventricular canal of the developing heart, and strongly but transiently in developing limbs. R-Spondins regulate Wnt/β-catenin by competing with the Wnt antagonist DKK-1 for binding to the Wnt co-receptors LRP-6 and Kremen, reducing their DKK-1-mediated internalization. Reports differ on whether R-Spondins bind LRP-6 directly.