title: Nutritional regulation of long-chain PUFA biosynthetic genes in rainbow trout (Oncorhynchus mykiss).
abstract: Most studies on dietary vegetable oil in rainbow trout (Oncorhynchus mykiss) have been conducted on a background of dietary EPA (20 : 5n-3) and DHA (22 : 6n-3) contained in the fishmeal used as a protein source in aquaculture feed. If dietary EPA and DHA repress their endogenous synthesis from α-linolenic acid (ALA, 18 : 3n-3), then the potential of ALA-containing vegetable oils to maintain tissue EPA and DHA has been underestimated. We examined the effect of individual dietary n-3 PUFA on the expression of the biosynthetic genes required for metabolism of ALA to DHA in rainbow trout. A total of 720 juvenile rainbow trout were allocated to twenty-four experimental tanks and assigned one of eight diets. The effect of dietary ALA, EPA or DHA, in isolation or in combination, on hepatic expression of fatty acyl desaturase (FADS)2a(Δ6), FADS2b(Δ5), elongation of very long-chain fatty acid (ELOVL)5 and ELOVL2 was examined after 3 weeks of dietary intervention. The effect of these diets on liver and muscle phospholipid PUFA composition was also examined. The expression levels of FADS2a(Δ6), ELOVL5 and ELOVL2 were highest when diets were high in ALA, with no added EPA or DHA. Under these conditions ALA was readily converted to tissue DHA. Dietary DHA had the largest and most consistent effect in down-regulating the gene expression of all four genes. The ELOVL5 expression was the least responsive of the four genes to dietary n-3 PUFA changes. These findings should be considered when optimising aquaculture feeds containing vegetable oils and/or fish oil or fishmeal to achieve maximum DHA synthesis.
authors.affiliation: 1Rheumatology Unit,Royal Adelaide Hospital,Adelaide,SA 5000,Australia.
authors.forename: Melissa K
authors.initials: MK
authors.lastname: Gregory
authors.affiliation: 2School of Life and Environmental Sciences,Deakin University,Warrnambool,VIC 3280,Australia.
authors.forename: Robert O
authors.initials: RO
authors.lastname: Collins
authors.affiliation: 3School of Natural Sciences,Institute of Aquaculture,University of Stirling,Stirling FK9 4LA,Scotland,UK.
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Tocher
authors.affiliation: 1Rheumatology Unit,Royal Adelaide Hospital,Adelaide,SA 5000,Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: James
authors.affiliation: 2School of Life and Environmental Sciences,Deakin University,Warrnambool,VIC 3280,Australia.
authors.forename: Giovanni M
authors.initials: GM
authors.lastname: Turchini
mesh_terms: D000123:Acetyltransferases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D004032:Diet / Q000662:veterinary; D004281:Docosahexaenoic Acids / Q000008:administration & dosage*; D015118:Eicosapentaenoic Acid / Q000008:administration & dosage*; D044943:Fatty Acid Desaturases / Q000235:genetics / Q000378:metabolism; D005260:Female; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D008099:Liver / Q000378:metabolism; D008297:Male; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D017962:alpha-Linolenic Acid / Q000008:administration & dosage*
chemical_list: D029941:Fish Proteins; D017962:alpha-Linolenic Acid; D004281:Docosahexaenoic Acids; D015118:Eicosapentaenoic Acid; D044943:Fatty Acid Desaturases; D000123:Acetyltransferases
keywords: ALA 
                    α-linolenic acid; DHA; DPA docosapentaenoic acid; Desaturase; ELOVL elongation of very long-chain fatty acid; Elongase; FADS fatty acyl desaturase; LC-PUFA long-chain PUFA; PUFA; n-3 Fatty acids