Two distinct insulins in the guinea pig: the broad relevance of these findings to evolution of peptide hormones.

In this paper we use the published data of others as well as our own recent data to question the widespread assumption that the gene for guinea pig insulin mutated rapidly after the divergence of guinea pigs from the main line of rodent evolution. We suggest that instead guinea pigs may have two pairs of alleles, one for typical guinea pig insulin, which is expressed in its pancreatic beta cells, and the other for a more typical mammalian insulin (designated rat/pork-type insulin), which is expressed in extrapancreatic cells. Further, we suggest the possibility that both pairs of genes may be evolutionarily very ancient and highly conserved. We also review evidence that the concept of nonallelic evolution may also apply to other hormones, including vasopressin, calcitonin, and growth hormone.