Long-chain polyunsaturated fatty acid synthesis in fish: Comparative analysis of Atlantic salmon (Salmo salar L.) and Atlantic cod (Gadus morhua L.) Δ6 fatty acyl desaturase gene promoters

Fish vary in the ability to biosynthesise n-3 long-chain polyunsaturated fatty acids (LC-PUFA), with marine fish such as cod being inefficient in comparison to freshwater and salmonid fish. We investigated differences in the gene promoters of Delta 6 fatty acyl desaturase (Delta 6 FAD), a critical enzyme in LC-PUFA biosynthesis, in cod and salmon. Progressive deletions and targeted mutations of the promoters were tested for activity in a transfected Atlantic salmon (AS) cell line under low or high LC-PUFA treatment, and regions sufficient to direct transcription were identified. Comparison of these regions with sequences of corresponding regions of Delta 6 FAD genes from mammals, amphibians and fish indicated a remarkable conservation of binding sites for SREBPs and NF-Y. In addition to these sites, a site was identified in salmon with similarity to that recognised by Sp1 transcription factor, and which was required for full expression of the salmon Delta 6 FAD gene. The cod promoter was less active and lacked the Sp1 site. Eicosapentaenoic acid suppressed LC-PUFA synthesis in AS cells and also suppressed activity of the salmon Delta 6 FAD promoter although this activity was likely mediated through sites other than Sp1, possibly similar to those recognised by NF-Y and SREBP transcription factors. (C) 2009 Elsevier Inc. All rights reserved.