Proglucagon cDNAs from the leopard frog, Rana pipiens, encode two GLP-1-like peptides

We have isolated and characterized proglucagon cDNAs from the intestine and pancreas of the leopard frog Rana pipiens. R. pipiens proglucagon encodes glucagon, glucagon-like peptides 2 (GLP-2), and two glucagon-like peptide 1 (GLP-1) like sequences. The pancreatic and intestinal cDNAs were of identical structure and sequence suggesting that, unlike many other non-mammalian vertebrates, there is little or no alternative splicing of the proglucagon mRNA in this species. A phylogenetic analysis of the GLP-1 encoding sequences implies that the exon encoding GLP-1 was triplicated early in frog evolution, more than 150 million years ago, before the divergence of modern frogs.