GPX2 and inflammatory bowel disease: In other examples, Hnf4a, a gene associated with epithelium renewal40, is more highly expressed in the base of the crypt in GF versus SPF mice, and Gpx2, whose deficiency is related to propagating IBD symptoms41, is induced in the region bordering epithelium and muscularis mucosae tissue in SPF versus GF mice (Supplementary Fig. 11).