COMPARISON OF GENE STRUCTURE, SEQUENCE HOMOLOGY AND EXPRESSION PATTERN OF LARGEMOUTH BASS GHRH-LP AND GHRH

Growth hormone releasing hormone (GHRH) is an important factor involved in growth hormone synthesis and secretion. In mammals, the GHRH and GHRH-LP are encoded by two separate genes. However, in non-mammalian vertebrates, it is believed that the GHRH-like peptide is the counterpart of GHRH in mammals. A real GHRH gene was discovered in goldfish and zebrafish recently. Its gene structure and expression distribution in teleost need to be further studied. In order to distinguish the characteristic of GHRH and GHRH-LP genes and further understand the GH secre-tion net in teleost, the cDNA sequences and genome gene structure of these two genes were determined in this study, and the gene expression pattern of GHRH and GHRH-like peptide in central nervous system, peripheral tissues and em-bryogenesis were compared respectively in largemouth bass (Micropterus salmoide). The results showed that both GHRH and GHRH-LP genes were consisted of 5 exons and 4 introns, and the exon-intron arrangement of genes were apparently different from each other, but showed conserved pattern with other vertebrates, respectively. The GHRH mature peptide was 27 amino acid length, which shared highly homologous with other vertebrates (74%100%); while GHRH-LP mature peptide was 44 amino acid length and showed mediate conservation with other vertebrate (41% 96%). The tissue distribution study showed that the GHRH mRNA expression was restricted in brain and medulla, and that GHRH-LP was widely distributed in central nerves and peripheral tissues. The GHRH mRNA was first detected at neural stage during embryogenesis period, and maintained at a high level during larval developing; GHRH-LP mRNA was first detected in blastula stage, and retain a considerable expression level at all the next stage examined. The results demonstrate that the GHRH and GHRH-LP are encoded by two different genes in largemouth bass.