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Great Lakes WATER Institute, University of Wisconsin–Milwaukee, Milwaukee, Wisconsin, USA 53204
1 Institute for Marine Biosciences, National Research Council, Halifax, Nova Scotia, Canada B3H 3Z1
2 Aquaculture Division, Fisheries and Oceans Canada, 4160 Marine Drive, West Vancouver, British Columbia, Canada V7V 1N6
3 Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
4 Centre for Biomedical Research, University of Victoria, Victoria, British Columbia, Canada V8W 3N5
(Requests for offprints should be addressed to R H Devlin; Email: devlinr{at}pac.dfo-mpo.gc.ca)
* Current address is Ocean Sciences Center, Memorial University of Newfoundland, St.John’s, Newfoundland, Canada A1C1S5
The objectives of this study are to examine hepatic gene expression changes caused by GH transgenesis and enhanced growth. This is the first use of cDNA microarrays to study the influence of GH transgenesis on liver gene expression in a non-mammalian vertebrate, and the first such study using sexually immature animals. Three groups of coho salmon were examined: GH transgenic on full ration (T), GH transgenic on restricted ration (R), and control non-transgenic (C). Specific growth rates for weight in T were approximately eightfold higher than in C, and fourfold higher than in R. Differential gene expression in T, R, and C samples was determined using ~3500 and 16 000 gene microarrays, and R and C samples were compared on a different ~4000 gene microarray. The use of multiple microarray platforms increased the overall proportion of the hepatic transcriptome considered in these studies. Cross-platform comparisons identified genes behaving similarly between studies. For example, genes encoding a precerebellin-like protein and complement component C3 were downregulated in R relative to C (R<C) in two microarray studies, and hemoglobins
and ß were R>C in all three studies. Comparisons of informative gene lists within and between studies inferred causes of altered gene expression. For example, ten genes, including 78 kDa glucose-regulated protein, glycerol-3-phosphate dehydrogenase, hemoglobins and ß, and a C-type lectin, were likely induced by GH transgenesis due to their presence in both T>C and R>C gene lists. Eleven genes, including hepcidin, nuclear protein p8, precerebellin-like, transketolase, and fatty acid-binding protein, were present in both T<C and R<C gene lists and were, therefore, likely suppressed by GH transgenesis. A large number of salmonid genes identified in these studies are involved in iron homeostasis, mitochondrial function, carbohydrate metabolism, cellular proliferation, and innate immunity. Pentose phosphate pathway genes phosphogluconate dehydrogenase, transaldolase, and transketolase, were dysregulated in GH transgenic samples relative to control samples. Changes in the expression of genes involved in maintaining hemoglobin levels (heme oxygenase, hemoglobins and ß, Kruppel-like globin gene activator, hepcidin) in R and T fish indicate a need for additional hemoglobin in the transgenic fish, perhaps due to higher metabolic rate required for enhanced growth.
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