Evolution and Pharmacology of Neuropeptide Y Receptors, Implications for vertebrate genome duplications

Abstract: The Y receptors comprise a family of evolutionarily related receptors belonging to the superfamily of G-protein coupled receptors (GPCR). Their natural ligands are in mammals neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP). These peptides have numerous physiological roles including induction of food intake, increase in blood pressure, inhibition of anxiety and control of circadian rythms. Both the Y receptor family and the peptide family have been proposed to have expanded in the two genome duplications suggested to have occurred early in vertebrate evolution. In this thesis further evidence is presented that support this scenario.A receptor was cloned in a primitive vertebrate, the river lamprey Lampetra fluviatilis. Phylogenetic analyses indicated that this receptor represents a pro-ortholog of Y4 and the fish receptorsYb and Yc. A novel subtype of the Y receptor family, most closely related to the Y2 subtype, was cloned from two different developmental lineages, teleost fish (zebrafish and rainbow trout) and amphibians (marsh frog and clawed frog). This receptor was tentatively called Y7.Site directed mutagenesis were used to study binding of the antagonist BIIE0246 to the human and chicken Y2 receptors. Three amino acids were predicted, and subsequently confimed, to be important for agonist binding.The Yb receptor from the rainbow trout was cloned and pharmacologicaly characterized. This pharamacological profile will facilitate future in-vivo studies of the NPY system in this species.The first y6 receptor from any non-mammalian species were cloned from chicken, Gallus gallus, and the tissue distribution profile was determined using reverse transcriptase PCR and an initial pharmacologigal characterization was also made.The melanocortin receptors, another GPCR family involved in food intake, were for the first time cloned from any non-tetrapod species. We cloned and characterized one MC3 and two MC5 receptors from the zebrafish Danio reiro. To conclude this thesis we present a theory for how the Y family of receptors were shaped during evolution by local and largescale duplications followed by geneloses, to result in the gene reportoir we see today.