Effects of domestication and growth hormone transgenesis on mRNA profiles in rainbow trout (Oncorhynchus mykiss)1

Abstract

Growth rate can be genetically modified in many vertebrates by domestication and selection and more recently by transgenesis overexpressing growth factor genes [e.g., growth hormone (GH)]. Although the phenotypic end consequence is similar, it is currently not clear whether the same modifications to physiological pathways are occurring in both genetic processes or to what extent they may interact when combined. To investigate these questions, microarray analysis has been used to assess levels of mRNA in liver of wild-type and growth-modified strains of rainbow trout (Oncorhynchus mykiss). This species has been used as a model because nondomesticated wild strains are available as comparators to assess genetic and physiological changes that have arisen both from domestication and from GH transgenesis. The analysis examined pure wild-type and pure domesticated strains as well as 2 different GH transgenes (with markedly different growth effects) both in pure wild and in wild × domesticated hybrid backgrounds. Liver mRNA showed highly concordant changes (Pearson correlations; r>0.828; P<0.001) in levels in domesticated and GH transgenic fish, relative to wild-type, for both up- and downregulated genes. Furthermore, among domesticated, transgenic, and their hybrid genotypes, a strong correlation (P<0.001) was found between growth rate and the number of genes affected (r=0.761 for downregulated mRNA and r=0.942 for upregulated mRNA) or between growth rate and mRNA levels relative to wild-type (r=0.931 for downregulated mRNA and r=0.928 for upregulated mRNA). One GH transgenic strain was found to affect growth and mRNA levels similar to domestication whereas effects of the other GH transgenic strain were much stronger. For both GH transgenes, a hybrid domesticated×wild background influenced growth rate and mRNA levels to only a small extent relative to the transgenes in a pure wild-type genetic background. Functional analysis found that genes involved in immune function, carbohydrate metabolism, detoxification, transcription regulation, growth regulation, and lipid metabolism were affected in common by domestication and GH transgenesis. The common responses of mRNAs in domesticated and GH transgenic strains is consistent with the GH pathway or its downstream effects being upregulated in domesticated animals during their modification from wild-type growth rates.