Probable hormone. Homodimer; disulfide-linked (PubMed:11358969, PubMed:15834545, PubMed:15155948). Heterodimer with RETNLG (PubMed:15834545). Strongly expressed in colon, and at lower levels in ileum (PubMed:15834545). In colon, found throughout the crypt and surface epithelium and in goblet cells (at protein level) (PubMed:15834545). Specific to the gastrointestinal tract; not detected in other tissues tested (PubMed:11209052, PubMed:15834545). Up-regulated in colon in response to a high-fat diet. Also up-regulated in obese mice mutant for the leptin receptor LEPR (db/db genotype). Belongs to the resistin/FIZZ family.