Evolutionary expression of glucose-dependent-insulinotropic polypeptide (GIP)

► Sea lamprey genomic analysis predicted a potential GIP-like gene although transcripts were not detected. ► GIP was detected in both the intestine and pancreas of the zebrafish and Xenopus laevis. ► GIP and insulin expression were limited to the intestine and pancreas, respectively, in chicken and mouse. ► Phylogenetic analysis supports the theory that GIP arose as a gene duplication of proglucagon.