Receptor for R-spondins that potentiates the canonical Wnt signaling pathway and acts as a stem cell marker of the intestinal epithelium and the hair follicle. Upon binding to R-spondins (RSPO1, RSPO2, RSPO3 or RSPO4), associates with phosphorylated LRP6 and frizzled receptors that are activated by extracellular Wnt receptors, triggering the canonical Wnt signaling pathway to increase expression of target genes. In contrast to classical G protein-coupled receptors, does not activate heterotrimeric G proteins to transduce the signal. Involved in the development and/or maintenance of the adult intestinal stem cells during postembryonic development. {ECO:0000269|PubMed:21693646, ECO:0000269|PubMed:21727895, ECO:0000269|PubMed:21909076, ECO:0000269|PubMed:22815884, ECO:0000269|PubMed:23809763}. This is the function of LGR5 (leucine rich repeat containing G protein-coupled receptor 5, ENSG00000139292).