Isolation, Characterization and Comparison of Atlantic and Chinook salmon Growth Hormone 1 and 2

Background: Growth hormone (GH) is an important regulator of skeletal growth, as well as other adapted processesin salmonids. The GH gene (gh) in salmonids is represented by duplicated, non-allelic isoforms designated as gh1 and gh2.We have isolated and characterized gh-containing bacterial artificial chromosomes (BACs) of both Atlantic and Chinooksalmon (Salmo salar and Oncorhynchus tshawytscha) in order to further elucidate our understanding of the conservationand regulation of these loci.Results: BACs containing gh1 and gh2 from both Atlantic and Chinook salmon were assembled, annotated, andcompared to each other in their coding, intronic, regulatory, and flanking regions. These BACs also contain the genesfor skeletal muscle sodium channel oriented in the same direction. The sequences of the genes for interferon alpha-1,myosin alkali light chain and microtubule associated protein Tau were also identified, and found in opposite orientationsrelative to gh1 and gh2. Viability of each of these genes was examined by PCR. We show that transposon insertions haveoccurred differently in the promoters of gh, within and between each species. Other differences within the promotersand intronic and 3'-flanking regions of the four gh genes provide evidence that they have distinct regulatory modes andpossibly act to function differently and/or during different times of salmonid development.Conclusion: A core proximal promoter for transcription of both gh1 and gh2 is conserved between the two species ofsalmon. Nevertheless, transposon integration and regulatory element differences do exist between the promoters of gh1and gh2. Additionally, organization of transposon families into the BACs containing gh1 and for the BACs containing gh2,are very similar within orthologous regions, but much less clear conservation is apparent in comparisons between thegh1- and gh2-containing paralogous BACs for the two fish species. This is consistent with the hypothesis that a burst oftransposition activity occurred during the speciation events which led to Atlantic and Pacific salmon. The Chinook andother Oncorhynchus GH1s are strikingly different in comparison to the other GHs and this change is not apparent in thesurrounding non-coding sequences.