MOLECULAR EVOLUTION OF GPCRS: Somatostatin/urotensin II receptors

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   Figure 1

   Alignment of SS sequences including their putative N-terminally extended forms from some representative vertebrate species. The overall structure of the SS precursors is shown. Conserved residues are shown in bold. Putative cleavage sites are enclosed by boxes. References correspond to GenBank or Ensembl accession numbers. For the non-annotated genes, the chromosomal location is indicated according to the Ensembl (ENS) or the Elephant Shark Genome Project (ESGP) data. SP, signal peptide; SS, somatostatin; LG, linkage group; sc, scaffold.
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   Figure 2

   Alignment of UII/URP sequences including their putative N-terminally extended forms from some representative vertebrate species. The overall structure of the UII/URP precursors is shown. Conserved residues are shown in bold. Putative cleavage sites are enclosed by boxes. References correspond to GenBank or Ensembl accession numbers. For the non-annotated genes, the chromosomal location is indicated according to the Ensembl (ENS) or the Elephant Shark Genome Project (ESGP) data. SP, signal peptide; U, UII/URP; LG, linkage group; sc, scaffold.
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   Figure 3

   Schematic organization of the putative ancestral paralogon bearing genes of the UII and SS families (adapted from Parmentier et al. (2011)).
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   Figure 4

   A proposed evolutionary scheme for the evolution of the genes of the SS and UII families in gnathostomes. Crossed-out boxes represent lost genes. The ancestral vertebrate had one SS gene and one UII gene that are thought to have arisen through local duplication. The two basal vertebrate tetraploidizations (1R and 2R) quadrupled each of these genes, whereupon the SS quartet lost one gene. Early in tetrapod evolution, the SS5, URP1, and URP2 genes were lost. In the actinopterygian lineage, the SS1 and SS2 genes were duplicated through local duplication. Then, the SS1 and UII genes were duplicated in the basal teleost tetraploidization (3R). No new SS2, SS5, URP, URP1, or URP2 genes emerged through the 3R event. In the chondrichthyan lineage, three genes of the ancestral SS quartet were apparently preserved, while only one gene of the UII family has been identified so far.
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   Figure 5

   Comparison of the amino acid sequences and predicted secondary structures of SS1 and UII with SS- and UII-like peptides from non-vertebrate species. Conserved residues are shown in bold. AllC, allatostatin C.
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   Figure 6

   Phylogeny of the six vertebrate SS receptor subtypes. The tree shows the phylogenetic relationships between human (Homo sapiens), mouse (Mus musculus), chicken (Gallus gallus), zebrafish (Danio rerio), and three-spined stickleback (Gasterosteus aculeatus) SSTR sequences. The phylogeny is based on a phylogenetic maximum-likelihood analysis (aLRT-supports, LG substitution model; Guindon et al. 2010). Branches with support lower than 80% have been collapsed. Grey branches mark 3R duplicates in teleost fish.
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   Figure 7

   Proposed evolutionary scheme for the evolution of the SSTR and UTS2R gene families in gnathostomes. Gene losses are indicated by crossed-out boxes. The ancestral vertebrate had two SSTR proto-orthologs located on different chromosomes; one gave rise to the SSTR1, SSTR4, and SSTR6 genes and another gave rise to the SSTR2, SSTR3, and SSTR5 genes. The ancestral UTS2R gene was located in the same chromosomal region as the SSTR2/3/5 ancestor. Thus, it is likely that the ancestral SSTR and UTS2R genes arose through a local duplication before the SSTR duplication that resulted in the SSTR2/3/5 and SSTR1/4/6 ancestors, followed by the translocation of the SSTR1/4/6 ancestor. The two basal vertebrate tetraploidizations (1R and 2R) quadrupled each of the receptor genes, whereupon the two SSTR quartets lost one gene each. In contrast, the UTS2R gene family acquired an additional member through a local duplication following the 2R event, resulting in five ancestral gnathostome UTS2R genes. Early in the evolution of tetrapods, the SSTR6 gene was lost and subsequently there have been differential losses of UTS2R genes in different tetrapod lineages, notably massive losses in the mammals. Only the non-avian reptiles have conserved all the five ancestral UTS2R genes. The loss of SSTR4 from the Anole lizard may be a secondary loss, as it can be found in the genomes of other non-avian reptiles (D Ocampo Daza, C Bergqvist and D Larhammar, unpublished observations) and birds. In the teleost lineage, SSTR4 was lost, while SSTR2, SSTR3, and SSTR5 were duplicated in the basal teleost tetraploidization (3R). No new SSTR1, SSTR6, or UTS2R genes emerged through the 3R event. The loss of UTS2R5 in zebrafish is probably a secondary loss as it can be found in other teleosts. Chromosome fusions and gene rearrangements in the teleost lineage moved some of the SSTR and UTS2R genes to the same chromosomes.
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   Figure 8

   Phylogeny of the five vertebrate UII receptor subtypes. The tree shows the phylogenetic relationships between UTS2R sequences in the same species as those in Fig. 6, with the addition of the Carolina anole lizard (Anolis carolinensis). Phylogenetic method followed was the same as that mentioned in Fig. 6. Branches with support lower than 80% have been collapsed.
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   Figure 9

   Schematic organization of the putative ancestral paralogons bearing genes of the SSTR and UTS2R families (adapted from Ocampo Daza et al. (2012)). The SSTR2, SSTR3 and SSTR5 genes, as well as the UTS2R genes, are located in the same paralogous regions (left). The SSTR1, SSTR4, and SSTR6 genes are part of a separate paralogon (right). Only a few of the neighboring gene families are shown in the figure as examples.

• © 2014 Society for Endocrinology