Abstract

Somatostatin (SS) and urotensin II (UII) are members of two families of structurally related neuropeptides present in all vertebrates. They exert a large array of biological activities that are mediated by two families of G-protein-coupled receptors called SSTR and UTS2R, respectively. It is proposed that the two families of peptides as well as those of their receptors likely derive from a single ancestral ligand-receptor pair. This pair had already been duplicated before the emergence of vertebrates to generate one SS peptide with two receptors, and one UII peptide with one receptor. Thereafter, each family expanded in the three whole genome duplications (1R, 2R and 3R) that occurred during vertebrate evolution whereupon some local duplications and gene losses took place. Following 2R, the vertebrate ancestor is deduced to have possessed three SS (SS1, SS2 and SS5) and six SSTR genes (SSTR1-6) on the one hand, and four UII (UII, URP, URP1 and URP2) and five UTS2R (UTS2R1-5) genes on the other. In the teleost lineage, all of these have been preserved with the exception of SSTR4. Moreover, several additional genes have been gained through 3R, such as SS4 and a second copy of the UII, SSTR2, -3 and -5 genes, and through local duplications, such as SS3. In mammals, all the genes of the SSTR family have been preserved, with the exception of SSTR6. In contrast, for the other families, extensive gene losses occurred since only SS1, SS2, UII, URP and one UTS2R gene are still present.