Characterization and modulation of gene expression and enzymatic activity of delta-6 desaturase in teleosts: A review

Abstract

To cite this version:Marie Vagner, Ester Santigosa. Characterization and modulation of gene expression and enzymatic activity of delta-6 desaturase in teleosts: A review.This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited.In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit:There is currently considerable interest in understanding how the biosynthetic pathways of highly unsaturated fatty acids (HUFA) are regulated in fish. The aim is to know if it is possible to replace fish oils (FO), rich in HUFA, by vegetable oils (VO), poor in HUFA and rich in their 18 carbon fatty acid precursors, in the feed of cultured fish species of commercial importance. Thus many studies have focussed on delta-6 desaturase (Δ6D) since it is the rate-limiting enzyme involved in HUFA biosynthesis from precursors. The aims of this paper were (i) to review and compare the structure, function, and tissue distribution of the Δ6D gene in teleosts and (ii) to review the effect of nutrition and environment on the modulation of Δ6D gene expression and on the activity of this enzyme in teleosts. Most existing studies have clearly shown that Δ6D is modulated by nutrition and environment in freshwater fish. This modulation allows the control of lipid metabolism and the maintenance of cell membrane functionality. Δ6D gene expression and enzymatic activity were higher in fish fed VO diets than in those fed FO diets, irrespective of their life cycle in seawater or freshwater; this concurs with expectations regarding the compensation for HUFA deficiency in VO. However, the magnitude of these increases was not great enough to maintain HUFA tissue content. Such a decrease in tissue content may result either from competition between substrates for Δ6D or from the inhibition of subsequent steps in HUFA biosynthesis, such as elongation or delta-5 desaturation activity. Other studies showed that Δ6D enzyme activity is stimulated at low temperatures and low salinities, which keep cell membranes fluid. In salmonids, Δ6D would then play an important role in the adaptation to salinity changes at parr-smolt transformation. In marine fish, similar nutritional and environmental modulations may occur, although conflicting data exist. A low expression of the Δ6D gene or the involvement of genetic, environmental, or hormonal factors could explain why Δ6D appears to be barely functional in marine fish. This review shows that, despite the large number of studies investigating the regulation of Δ6D, little is kno...

Regulation of metabolism by dietary carbohydrates in two lines of rainbow trout divergently selected for muscle fat content

“…Looking further along the fatty acid bioconversion pathway, we did not find any effect of dietary carbohydrate on the expression of another desaturase, the D6D, contrary to Seiliez et al (Seiliez et al, 2001). The high level of fish oil and fish meal in the diets probably supplied enough of the essential fatty acids (Vagner and Santigosa, 2010). In the adipose tissue, we found no stimulatory effect of dietary carbohydrates on the expression of lipogenic enzymes, as has been reported in catfish (Likimani and Wilson, 1982), confirming the lack of response in salmonids to dietary manipulations (Lin et al, 1977a;Lin et al, 1977b).…”

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“…Although the requirements vary greatly between species, in general, marine fish have a barely functional enzymatic pathway for converting ALA (18:3n-3) and linoleic acid (LA, 18:2n-6) into EPA, DHA and ARA, meaning that they require preformed EPA, DHA and ARA, whereas freshwater fish only require the precursors (Vagner and Santigosa, 2011). Salmon is an anadromous fish species: salmon begin their life in freshwater and then migrate to the sea for most of their growth period before returning to freshwater to breed.…”

Omega-3 long-chain polyunsaturated fatty acids and aquaculture in perspective

“…The expression of Δ6 and Δ5 desaturase and some elongase genes are subject to nutritional regulation and are up-regulated, generally by up to 2-3-fold, in fish fed VO-based diets compared to fish fed FO-based diets (Leaver et al, 2008a;Torstensen and Tocher, 2011;Vagner and Santigosa, 2011) and this has been shown to produce a similar increase in LC-PUFA biosynthesis in liver and intestinal tissues in salmonids (Zheng et al, 2004(Zheng et al, , 2005Torstensen and Tocher, 2011).…”