Promoter analysis of a growth hormone transgene in Atlantic salmon

Abstract

The ocean pout ( Macrozoarces americanus) op5a antifreeze protein gene promoter has been used to generate a line of growth hormone (GH) transgenic Atlantic salmon with greatly enhanced growth rates. A study of the genomically integrated GH transgene (EO-1α) in this line of salmon revealed that the first 1579 bp of the 2115-bp promoter was deleted and relocated downstream of the GH coding region, raising questions regarding the ability of the truncated promoter to drive expression of the GH transgene and the potential influence of the relocated 5′ promoter region. In this study, 11 promoter constructs were fused to a luciferase reporter gene, and their transcriptional ability was examined after transfection into salmon and human cell lines cultured at 21 and 37 °C, respectively. Construct expression was similar in all cell lines, apart from those of less than 266 bp, where expression in the salmon cells greatly exceeded that of the human cells. The results demonstrated the presence of positive and negative regulatory regions within the promoter that would allow the regulation of gene expression at multiple sites. Removal of the first 1579 bp from the promoter resulted in a 70% loss of the luciferase expression exhibited by the full-length promoter, whereas ligating the deleted 5′ promoter sequence downstream of the luciferase reporter gene only restored approximately 10% of this loss. These results suggested that in vivo expression of the EO-1α transgene is driven by elements within the weak truncated promoter in conjunction with the relocated 5′ promoter region.