Molecular Cloning, Characterization, and Nutritional Regulation of Elovl6 in Large Yellow Croaker (Larimichthys crocea)

Abstract

Elongation of very long chain fatty acids protein 6 (Elovl6) is a key enzyme in fatty acid synthesis, which participates in converting palmitate (C16:0) to stearate (C18:0). Although studies of Elovl6 have been carried out in mammals, the nutritional regulation of elovl6 in fish remains poorly understood. In the present study, the cloning and nutritional regulation of elovl6 were determined in large yellow croaker. Sequence and phylogenetic analysis revealed that the full-length cDNA of elovl6 was 1360 bp, including an open reading frame of 810 bp encoding a putative protein of 269 amino acid that possesses the characteristic features of Elovl proteins. The transcript level of elovl6 was significantly increased in the liver of croaker fed the diets with soybean oil (enriched with 18: 2n-6, LA) or linseed oil (enriched with 18: 3n-3, ALA) than that in croaker fed the diet with fish oil (enriched with 20: 5n-3 and 22: 6n-3). Correspondingly, the elovl6 expression in croaker’s hepatocytes treated with ALA or LA was remarkably increased compared to the controls. Furthermore, the transcription factors including hepatocyte nuclear factor 1α (HNF1α), CCAAT-enhancer-binding protein β (CEBPβ), retinoid X receptor α (RXRα), and cAMP response element-binding protein 1 (CREB1) greatly enhanced promoter activity of elovl6 in large yellow croaker, and the expression of transcription factors is consistent with the changes of elovl6 expression in response to fatty acids in vivo and in vitro. In conclusion, this study revealed that elovl6 expression in large yellow croaker could be upregulated by dietary ALA or LA via the increased transcriptional expression of transcription factors including hnf1α, cebpβ, rxrα, and creb1.

Molecular Characterization, Nutritional and Insulin Regulation of Elovl6 in Rainbow Trout (Oncorhynchus mykiss)

“…In the present study, ORF of Elovl6 was cloned from the rainbow trout, which possessed the histidine box (HXXHH) and six membrane-spanning domains of Elovl proteins [16], and showed high identity (87%) with mammals and teleost. In rainbow trout, the high expression level of elovl6 was observed in brain and liver tissues, which is consistent with the results in mice [2,4,5] and large yellow croaker [7].…”

“…Hence, the large amount of PA and POA in FO may promote the expression level of elovl6 in rainbow trout to drive the synthesis of fatty acids [18]. A similar effect of PA on elovl6 expression was also observed in large yellow croaker [7]. Furthermore, the transcriptional expression of elovl6 in hepatocytes of rainbow trout treated with EPA and DHA was also higher than that in the ALA and LA groups, which may be another evidence for the high expression level of elovl6 in the FO group.…”

“…In the present study, the expression of elovl6 in the liver of rainbow trout that were fed diets containing FO was higher than that in the SO and LO groups. Our studies showed that fish oil in diets is richer in PA, POA, EPA, and DHA than soybean oil and linseed oil [7]. PA and POA are the substrates for the synthesis of C18:0 and C18:1n-7 [17].…”

“…Loss of Elovl6 function reduced the concentrations of C18:0 and C18:1n-7, but increased C16:0 and C16:1n-7 contents in mice (Mus musculus) [6], and dietary fatty acids (PUFAs) could profoundly regulate the expression of elovl6 in mice [5]. In the large yellow croaker (Larimichthys crocea), elovl6 expression was increased with the replacement of fish oil by soybean oil or linseed oil in diets via the regulation of transcription factors including hepatocyte nuclear factor 1α (HNF1α), CCAAT-enhancer-binding protein β (CEBPβ), retinoid X receptor α (RXRα), and cAMP response element-binding protein (CREB1) [7]. Furthermore, Elovl6 also showed a crucial function for insulin resistance [3].…”

“…The deletion of elovl6 in mice could prevent diet-induced insulin resistance, and specific deletion of elovl6 in leptin receptor-deficient mice increased insulin adaptability [3,8]. However, in aquatic animals, Elovl6 was only cloned in Misgurnus anguillicaudatus [9], Eriocheir sinensis [10], and Larimichthys crocea [7] to date, the regulation of dietary fatty acids or insulin on elovl6 expression is still poorly understood.…”