MOLECULAR EVOLUTION OF GPCRS: Secretin/secretin receptors

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   Figure 1

   (A) Alignment of secretin mature peptides. Accession numbers are human Homo sapiens, AAG31443; sheep Ovis aries, P31299; rat Rattus norvegicus, AAA42128; domestic guinea pig Cavia porcellus, P63297; mouse Mus musculus, CAA51982; cattle Bos taurus, P63296; dog Canis lupus familiaris, P09910; rabbit Oryctolagus cuniculus, P32647; pig Sus scrofa, AAA31121; chicken Gallus gallus, P01280; zebra finch Taeniopygia guttata, ENSTGUT00000007450; turkey Meleagris gallopavo, ENSMGAT00000004169; African clawed frog Xenopus laevis, NP_001267540; bullfrog Rana rugulosa, ADT91712. *Predicted sequence from Ensembl.org. (B) Percent amino acid sequence identity of the aligned secretin mature peptides.
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   Figure 2

   Comparison of gene organizations of secretin in avians and mammals. The exons are shown as boxes and the introns as lines. The lengths of the exons and introns are not drawn to scale so that they can be aligned between genes.
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   Figure 3

   Phylogenetic analysis of the secretin/glucagon hormone precursor superfamily. The tree was generated by maximum likelihood (ML) and plotted by MEGA 5.0. Predicted sequences are marked by asterisk. SCT, secretin precursor; preproGHRH, prepro-growth hormone-releasing hormone; PHI–VIP, peptide histidine isoleucine–vasoactive intestinal peptide precursor; PRP–PACAP, pituitary adenylate cyclase-activating polypeptide (PACAP)-related peptide–PACAP precursor. The proposed primordial exon is represented by a black rectangle.
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   Figure 4

   Chromosomal locations of SCT genes in various vertebrate species. Neighboring genes of SCT in different vertebrate genomes are shown. Homologous genes in proximity of secretin are linked by straight lines to demonstrate the syntenic gene environment of SCT in the analyzed vertebrate species. Note that sct is not found in zebrafish genome. Versions of genome databases at Ensembl: human (GRCh37), mouse (GRCm38), zebra finch (taeGut3.2.4), chicken (Galgal4), Xenopus tropicalis (JGI_4.2), and zebrafish (Zv9).
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   Figure 5

   Phylogenetic analysis of the secretin receptor superfamily. The predicted sequence from genome project is marked by an asterisk. Other receptor sequences used in the present analysis are referenced (Cardoso et al. 2006, Ng et al. 2010, Wang et al. 2012, Hwang et al. 2013).
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   Figure 6

   Alignment of the amino acid sequences of secretin receptors in post-2R vertebrates. The conservation scoring is performed by PRALINE. The score ranged from zero (unconserved) to ten (most conserved) and represented with the color assignment from blue to red. Homo sapiens human, Danio rerio zebrafish, Gallus gallus chicken, Xenopus laevis African clawed frog, and Protopterus dolloi lungfish.
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   Figure 7

   Summary of secretin and secretin receptors characterized at present. The hypothetical timing of the two rounds of whole-genome duplications (1R and 2R) (Ogino et al. 2009) and the teleost-specific genome duplication (TSGD) are indicated by a green dot on the phylogeny of the vertebrate lineage. Major events in the evolution of SCT are marked by a yellow diamond and explained with diagrams and description. It is hypothesized that SCT genes were deleted in teleosts and lungfish (Hwang et al. 2013). The cross represents the absence of the genes. Color-filled hexagons represent the presence of a bioactive gene while the white-filled hexagon represents the presence of a gene which may not be bioactive.

• © 2014 Society for Endocrinology