MOLECULAR EVOLUTION OF GPCRS: Ghrelin/ghrelin receptors

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   Figure 1

   Molecular phylogenetic tree of the ghrelin receptor (GHS-R1a) family in humans. The phylogenetic tree of amino acid (AA) sequences was constructed by using the neighbor-joining (NJ) method with MEGA4 (http://www.megasoftware.net/). The numbers on the branch points are the bootstrap values (as percentages based on 1000 replicates). AA sequences obtained from the NCBI BLAST (http://blast.ncbi.nlm.nih.gov/Blast.cgi). Abbreviations and accession numbers indicate as follows: MLNR: motilin receptor (NM_001507), NMUR1 and 2: neuromedin-U receptor 1 and 2 (NM_006056 and NM_020167), and NTSR1 and 2: neurotensin receptor 1 and 2 (NM_002531 and NM_012344), and GPR39 (NM_001508).
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   Figure 2

   Molecular phylogenetic tree of the ghrelin receptor (GHS-R1a) in mammals. The phylogenetic tree of amino acid (AA) sequences was constructed by using the neighbor-joining (NJ) method with MEGA4 Software (http://www.megasoftware.net/). The numbers on the branch points are the bootstrap values (as percentages based on 1000 replicates). AA sequences obtained from the Ensembl Genome Browser (http://www.ensembl.org/index.html). GeneID shows the following species name. Receptors for human motilin (MLNR), neuromedin-U (NMUR1), and neurotensin (NTSR1) were used as the out group. Symbols are defined as follows: closed circle, Euarchontoglires; open square, Afrotheria; asterisk, Marsupialia; open down triangle, Laurasiatheria.
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   Figure 3

   Molecular phylogenetic tree of GHS-Ra and GHS-R1a-LR in nonmammalian vertebrates. The phylogenetic tree of amino acid (AA) sequences was constructed by using the neighbor-joining (NJ) method with MEGA4 (http://www.megasoftware.net/). The numbers on the branch points are the bootstrap values (as percentages based on 1000 replicates). The scale bar indicates the average number of substitutions per position (a relative measure of evolutionary distance). AA sequences obtained from the NCBI BLAST (http://blast.ncbi.nlm.nih.gov/Blast.cgi) or the Ensembl Genome Browser (http://www.ensembl.org/index.html). Accession number of the gene or GeneID shows the following species name. Receptors for human motilin (MLNR), neuromedin-U (NMUR1), and neurotensin (NTSR1) were used as the out group.
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   Figure 4

   Schematic diagram of the evolution of the ghrelin receptor in vertebrates. The scheme includes data for Cyclostomata (Agnathans) and elephant shark (Chondrichthyes). The question marks indicate the possibility that an amino acid fragment of their receptor is GHS-R1a or an ancestral type of GHS-R. The three whole-genome duplication (WGD) events are shown by yellow stars. Polyploidization that occurred in some teleost species of Actinopterygii is shown by orange stars. The GHS-Ra and its isoforms are found in physostomous fish, which have the anlage of lungs, and tetrapods, which have lungs. In contrast, the GHS-R1a-LR and its isoforms are found in physoclistious fish, which have swim bladders that are not connected to the alimentary tract.
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   Figure 5

   Schematic diagram of the evolution of ghrelin. In elasmobranchs, HH shark, and BTR shark denote hammerhead shark and blacktip reef shark respectively. In each ghrelin amino acid (AA) sequence, light blue letters indicate AAs that have fatty acid modifications, and red or blue letters indicate AAs that have a positive or negative charge respectively. The carboxyl terminus of ghrelin in teleosts is amidated. Fatty acid modification is also indicated with a green symbol on the first sequence in each group. In elasmobranchs, in addition to the acyl modification, ghrelin-like peptide of stingray has an additional modification by mucin-type carbohydrate chains, as shown in the purple symbols (Kaiya et al. 2009c). Some ghrelin molecules have truncated C-termini due to the post-translational processing. However, the presence of isoforms with AA substitutions has not been identified, even in fish species where polyploidization of the ghrelin receptor is seen.

• © 2014 Society for Endocrinology