R-Spondin 1 （RSPO1, Roof plate-specific Spondin 1）, also known as cysteine-rich and single thrombospondin domain containing protein 3 （Cristin 3）, is a 27-30 kDa secreted protein that shares ~40% amino acid （aa） identity with three other R-Spondin family members. RSPO1 is a secreted activator protein with two cystein-rich, furin-like domains and one thrombospondin type 1 domain. R-Spondin 1 is expressed in early development at the roof plate boundary and is thought to contribute to dorsal neural tube development. Injection of recombinant R-Spondin 1 in mice causes activation of beta-catenin and proliferation of intestinal crypt epithelial cells, and ameliorates experimental colitis. Interest in R-Spondin 1 as a cell culture supplement has grown with the expansion of the organoid field. R-Spondin 1 is widely used in organoid cell culture workflows as a vital component that promotes both growth and survival of 3D organoids.