Recombinant R-spondin 1 LR5 protein is engineered to act as a high affinity ligand for the LGR5 receptor.  In epithelial tissues LGR5 marks the stem cell population.  This engineered protein, R-spondin 1 LR5, activates wnt signalling only in the LGR5+ stem cell population.  R-spondin1 LR5 has been tested in intestinal organoid culture and supports organoid survival and growth. As LGR5 specifically marks stem cells and is not found on transit amplifying cells, the lower crypt multiplicity seen in organoid cultures with R-spondin 1 LR5 (in comparison to wild-type R-spondin 1, Qk006) supports the notion that this engineered form is acting specifically on stem cells.  This specialized form of R-spondin 1 was developed in Marc de la Roche’s lab (University of Cambridge).