Discription：R-Spondin 1, also known as cysteine-rich and single thrombospondin domain containing protein 3 （Cristin 3） , is a 27kDa secreted protein that shares ～40％ amino acid （aa） identity with three other R-Spondin family members （1, 2） . All R-Spondins regulate Wnt/beta-Catenin signaling but have distinct expression patterns. R-Spondin 1 competes with the Wnt antagonist DKK-1 for binding to the Wnt co-receptors, Kremen and LRP-6, reducing their DKK-1-mediated internalization. However, reports are mixed on whether R-Spondin 1 binds LRP-6 directly. R-Spondin 1 is expressed in early development at the roof plate boundary and is thought to contribute to dorsal neural tube development. I Postnatally, R-Spondin 1 is expressed by neuroendocrine cells in the intestine, adrenal gland and pancreas, and by epithelia in kidney and prostate （9） . Injection of recombinant R-Spondin 1 in mice causes activation of beta-catenin and proliferation of intestinal crypt epithelial cells, and ameliorates experimental colitis. Mouse R-Spondin 1 shares 98％, 94％, 94％, 93％, 92％ and 88％ aa identity with rat, human, horse, cow, goat and dog RSPO-1, respectively, within aa 21-209. Recombinant Mouse R-Spondin 1 is a single non-glycosylated polypeptide chain containing 189 amino acids
