title: Highly unsaturated fatty acid synthesis in marine fish: cloning, functional characterization, and nutritional regulation of fatty acyl delta 6 desaturase of Atlantic cod (Gadus morhua L.).
abstract: This study reports the cloning, functional characterization, tissue expression, and nutritional regulation of a delta6 fatty acyl desaturase of Atlantic cod (Gadus morhua). PCR primers were designed based on the sequences of conserved motifs in available fish desaturases and used to isolate a cDNA fragment from cod liver, with full-length cDNA obtained by rapid amplification of cDNA ends. The cDNA for the putative desaturase was shown to comprise 1980 bp, including a 261-bp 5'-UTR, a 375-bp 3'-UTR, and an ORF of 1344 bp that specified a protein of 447 amino acids. The protein sequence included three histidine boxes, two transmembrane regions, and an N-terminal cytochrome b5 domain containing the heme-binding motif HPGG, all characteristic of microsomal fatty acyl desaturases. The cDNA displayed delta6 desaturase activity in a yeast expression system. Quantitative real-time PCR assay of gene expression in cod showed that the delta6 desaturase gene was expressed highly in brain, to a slightly lesser extent in liver, kidney, intestine, red muscle, and gill, and at much lower levels in white muscle, spleen, and heart. The expression of the delta6 desaturase gene did not appear to be under significant nutritional regulation, with levels in liver and intestine being barely altered in fish fed a vegetable oil blend, in comparison with levels in fish fed fish oil. This was reflected in enzyme activity, as hepatocytes or enterocytes showed very little highly unsaturated FA biosynthesis activity irrespective of diet. Further studies are required to determine why the delta6 desaturase appears to be barely functional in cod under the conditions tested.
authors.affiliation: Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, Scotland, United Kingdom. d.r.tocher@stir.ac.uk
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Tocher
authors.forename: Xiaozhong
authors.initials: X
authors.lastname: Zheng
authors.forename: Christian
authors.initials: C
authors.lastname: Schlechtriem
authors.forename: Nicola
authors.initials: N
authors.lastname: Hastings
authors.forename: James R
authors.initials: JR
authors.lastname: Dick
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Teale
mesh_terms: D000595:Amino Acid Sequence; D000821:Animal Feed; D000818:Animals; D003001:Cloning, Molecular; D004041:Dietary Fats / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000096:biosynthesis*; D005395:Fish Oils / Q000378:metabolism; D048389:Gadus morhua; D050602:Linoleoyl-CoA Desaturase / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D008969:Molecular Sequence Data; D010938:Plant Oils / Q000378:metabolism
chemical_list: D004041:Dietary Fats; D005231:Fatty Acids, Unsaturated; D005395:Fish Oils; D010938:Plant Oils; D050602:Linoleoyl-CoA Desaturase