Molecular cloning, tissue expression and regulation of Liver X Receptor (LXR) transcription factors of Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss)

• Published in: Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology
• Main Authors: Cruz-Garcia, Lourdes, Minghetti, Matteo, Navarro, Isabel, Tocher, Douglas R
• Other Authors: Universitat de Barcelona, Institute of Aquaculture, orcid:0000-0002-8603-9410
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2009
• Subjects: Atlantic salmon; Rainbow trout; liver X receptor; transcription factors; lipid metabolism; LXR genes; gene expression; vegetable oil; cholesterol; fish oil; nutritional regulation; Salmo salar
• Online Access: http://hdl.handle.net/1893/1827; https://doi.org/10.1016/j.cbpb.2009.02.001; http://www.sciencedirect.com/science/journal/10964959; http://dspace.stir.ac.uk/bitstream/1893/1827/1/Salmonid%20LXRs%20revised.pdf

Fish are important sources of high quality protein, essential minerals such as iodine and selenium, vitamins including A, D and E, and omega-3 fatty acids in the human diet. With declining fisheries worldwide, farmed fish constitute an ever-increasing proportion of fish in the food basket. Sustainable development of aquaculture dictates that diets will have to contain increasing levels of plant products that are devoid of cholesterol, but contain phytosterols that are known to have physiological effects in mammals. Liver X receptors (LXR) are transcription factors whose activity is modulated by sterols, with activation inducing cholesterol catabolism and de novo fatty acid biosynthesis in liver. Transcriptomic analysis has shown that substitution of fish meal and oil with plant products induces genes of cholesterol and fatty acid metabolism in salmonids. Here we report the cloning of LXR cDNAs from two species of salmonid fish that are important in aquaculture. The full-length cDNA (mRNA) of LXR obtained from salmon was shown to be 3766 bp, which included a 5’-untranslated region (UTR) of 412 bp and a 3’-UTR of 1960 bp and an open reading frame (ORF) of 1394 bp, which specified a protein of 462 amino acids. The trout LXR full-length cDNA was 2056 bp, including 5’- and 3’-UTRs of 219 and 547 bp, respectively, and an ORF of 1290 bp, which specified a protein of 427 amino acids. The protein sequences included characteristic features of mammalian LXRs, including the DNA binding (DBD), containing P-box, ligand binding (LBD) and activation function-2 (AF-2) domains, D-box, D (hinge) region, and eight cysteines that belong to the two zinc fingers. Phylogenetic analysis clustered the salmonid LXRs together, more closely with zebrafish and more distantly from medaka and stickleback. A pair-wise comparison among vertebrate LXR sequences showed the amino acid sequence predicted by the salmon LXR ORF showed greatest identity to that of trout 97%, and 97%, 87% and 81% identity to LXRs of zebrafish, frog and human (LXRα). The ...