Sterol regulatory element binding protein and Sp1 is required for transcriptional activation of a freshwater carnivorous fish (Channa striata) elovl5 elongase

Abstract

Long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis involves the activities of two groups of enzymes, the fatty acyl desaturases (Fads) and elongases of very long-chain fatty acid (Elovl). Fish are major source of beneficial n-3 LC-PUFA in human diet and there is a considerable interest to elucidate the mechanism and regulatory aspects of LC-PUFA biosynthesis in farmed fish species. The promoter of elovl5 elongase, which catalyze the rate limiting reaction of adding two carbons to the C18 PUFA have been previously described and characterized from several marine and diadromous teleost species. We report here the cloning and characterization of the elovl5 promoter from two freshwater fish species, the carnivorous snakehead fish (Channa striata) and zebrafish. Results show the importance of sterol regulatory element binding protein (Srebp) and the corresponding sterol responsive element (SRE) in the core regulatory region of both promoters. Mutagenesis luciferase and electrophoretic mobility shift assays confirm that SRE is indispensable for basal transcriptional activation in both species. In addition, several Sp1 binding sites located in close proximity with SRE were present in the snakehead promoter, with one having a potential synergy with SRE in regulating elovl5 expression. The core elovl5 promoter fragments of both species also directed in vivo expression in the yolk syncytial layer of developing zebrafish embryos. This study is the first functional promoter analysis of Elovl5 in freshwater teleost.