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PLoS One April 1, 2011; 6 (4): e19384.
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Origin of secretin receptor precedes the advent of tetrapoda: evidence on the separated origins of secretin and orexin.

Tam JK , Lau KW , Lee LT , Chu JY , Ng KM , Fournier A , Vaudry H , Chow BK .

At present, secretin and its receptor have only been identified in mammals, and the origin of this ligand-receptor pair in early vertebrates is unclear. In addition, the elusive similarities of secretin and orexin in terms of both structures and functions suggest a common ancestral origin early in the vertebrate lineage. In this article, with the cloning and functional characterization of secretin receptors from lungfish and X. laevis as well as frog (X. laevis and Rana rugulosa) secretins, we provide evidence that the secretin ligand-receptor pair has already diverged and become highly specific by the emergence of tetrapods. The secretin receptor-like sequence cloned from lungfish indicates that the secretin receptor was descended from a VPAC-like receptor prior the advent of sarcopterygians. To clarify the controversial relationship of secretin and orexin, orexin type-2 receptor was cloned from X. laevis. We demonstrated that, in frog, secretin and orexin could activate their mutual receptors, indicating their coordinated complementary role in mediating physiological processes in non-mammalian vertebrates. However, among the peptides in the secretin/glucagon superfamily, secretin was found to be the only peptide that could activate the orexin receptor. We therefore hypothesize that secretin and orexin are of different ancestral origins early in the vertebrate lineage.

PubMed ID: 21559418
PMC ID: PMC3084839
Article link: PLoS One

Species referenced: Xenopus laevis
Genes referenced: adcyap1 adcyap1r1 gcg gprc6a hcrt prnp pth sctr vip vipr1 vipr2

Article Images: [+] show captions
References [+] :
Abascal, ProtTest: selection of best-fit models of protein evolution. 2005, Pubmed