188宝金博页面版

Fish Physiology and Biochemistry vol. 7 nos 1-4 pp 381-385 (1989)Kugler Publications, Amsterdam/BerkeleyEvolutionary implications of two rainbow trout growth hormone genesT.T. Chen,l , 2 L.B. Agellon, 3C.M. Lin,1H.J. Tsai,lPeijun Zhang,4L.I. Gonzlez-Villasenor 4 andD.A. Powersl , 4ICenter of Marine Biotechnology, The University of Maryland, Baltimore, MD 21202, U.S.A.;2 Department of Zoology, The University of Maryland, College Park, MD 21476, U.S.A.; 3 ColumbiaUniversity College of Physicians and Surgeons, New York, N. Y. 10032, U.S.A; 4 Department of Biology,The Johns Hopkins University, Baltimore, MD 21218, U.S.A.Keywords: growth hormone gene, rainbow trout, evolution, teleosts, recombinant DNA, nucleotidesubstitutions, growth hormone cDNAAbstractThe primary structures of two rainbow trout growth hormone mRNAs (GHI and GH2) have been deducedby direct sequencing of their respective cDNA clones and portions of the mRNA. Both GH 1 and GH2 mRNAcontain open reading frames comprised of 630 nucleotides and encode 210 amino acid residues of which 11are variant. The translated regions of both mRNA are flanked by a short but rather conserved 5'-end, anda relatively long but highly diverged 3'-end. The differences at translated and 3' -untranslated regions suggestthat the GH 1 and GH2 mRNA originate from different loci. The GH 1 and GH2 mRNA are likely transcribedfrom two distinct loci which were duplicated during tetraploidization of salmonid genome between 50 to 100million years ago.The GH2 gene has been isolated and sequenced from a rainbow trout genomic library. This gene spansa region of approximately 4 kilobases. The trout GH gene is comprised of 6 exons and 5 introns, in contrastto 5 exons and 4 introns in mammals. The additional intron in the trout gene interrupts the translated regionsthat are analogous to the last exon of the mammalian counterpart. The alleged internally repeating sequencesin mammalian GH, prolactin (Prl) and placental lactogen (PL) are not observed in the predicted polypeptidesequence of trout GH. In addition, direct repeats that flank exons I, III and V of mammalian GH, Prl andPL genes are absent in trout gene. These findings indicate that the rainbow trout GH gene structure doesnot support the current hypothesis that internally repeated regions in GH, Prl and PL arose from a smallprimordial gene.IntroductionGrowth hormone (GH) is a single chain polypeptideof about 22 kDa, produced by the somatotrophs inthe anterior portion of the pituitary gland. Theprimary function of this hormone is to promote so-matic growth in vertebrates. GH polypeptide hasbeen isolated from fishes (Farmer et al. 1976a;Farmer et al. 1981; Cook et al. 1983; Wagner et al.1985; Kawauchi et al. 1986), reptiles (Farmer et al.1976b), amphibians (Farmer et al. (1976b), birds(Farmer et al. 1974), and mammals (see Nicoll et al.1986). GH from these species show similarities inbiological, biochemical and physicochemical prop-erties. Immunochemical studies have also revealeda high degree of relatedness among GH's of primi-tive fishes, reptiles, amphibians, birds and mam-mals (Hayashida 1970; Hayashida et al. 1975),however, GH of teleosts appear to be more diver-gent.The structure and regulation of GH, prolactin(Prl) and placental lactogen (PL) genes in mam-