title: Medaka receptors for somatolactin and growth hormone: phylogenetic paradox among fish growth hormone receptors.
abstract: Somatolactin (SL) in fish belongs to the growth hormone/prolactin family. Its ortholog in tetrapods has not been identified and its function(s) remains largely unknown. The SL-deficient mutant of medaka (color interfere, ci) and an SL receptor (SLR) recently identified in salmon provide a fascinating field for investigating SL's function(s) in vivo. Here we isolated a medaka ortholog of the salmon SLR. The mRNA is transcribed in variable organs. Triglycerides and cholesterol contents in the ci are significantly higher than those in the wild type, providing the first evidence of SL's function in suppressing lipid accumulation to organs. Interestingly, phylogenetic comparisons between the medaka SLR and growth hormone receptor (GHR), which is also isolated in this study, in relation to GHRs of other fish, suggested that all GHRs reported from nonsalmonid species are, at least phylogenetically, SLRs. An extra intron inserted in medaka and pufferfish SLRs and flounder and sea bream GHRs also supports their orthologous relationship, but not with tetrapod GHRs. These results may indicate lineage-specific diversification of SLR and GHR functions among fish or just an inappropriate naming of these receptors. Further functional and comparative reassessments are necessary to address this question.
authors.affiliation: Department of Integrated Biosciences, University of Tokyo, Kashiwa-shi, Chiba 277-8562, Japan. shoji.fukamachi@uni-konstanz.de
authors.forename: Shoji
authors.initials: S
authors.lastname: Fukamachi
authors.forename: Takashi
authors.initials: T
authors.lastname: Yada
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Mitani
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D016000:Cluster Analysis; D019295:Computational Biology; D029941:Fish Proteins / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism; D050356:Lipid Metabolism; D008969:Molecular Sequence Data; D009990:Oryzias / Q000235:genetics*; D010802:Phylogeny; D010907:Pituitary Hormones / Q000378:metabolism; D011979:Receptors, Pituitary Hormone / Q000235:genetics* / Q000378:metabolism; D011986:Receptors, Somatotropin / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D029941:Fish Proteins; D006023:Glycoproteins; D010907:Pituitary Hormones; D011979:Receptors, Pituitary Hormone; D011986:Receptors, Somatotropin; C064448:somatolactin protein, fish