, Volume 41, Issue 11, pp 1003–1016 | Cite as

Highly unsaturated fatty acid synthesis in marine fish: Cloning, functional characterization, and nutritional regulation of fatty acyl Δ6 desaturase of Atlantic cod (Gadus morhua L.)

  • Douglas R. Tocher
  • Xiaozhong Zheng
  • Christian Schlechtriem
  • Nicola Hastings
  • James R. Dick
  • Alan J. Teale


This study reports the cloning, functional characterization, tissue expression, and nutritional regulation of a Δ6 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 Δ6 desaturase activity in a yeast expression system. Quantitative real-time PCR assay of gene expression in cod showed that the Δ6 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 Δ6 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 Δ6 desaturase appears to be barely functional in cod under the conditions tested.



fish oil


highly unsaturated FA (carbon chain length≥C20 with≥3 double bonds)


open reading frame


quantitative real-time polymerase chain reaction


rapid amplification of cDNA ends


Saccharomyces cerevisiae minimal medium minus uracil


universal primer mix


untranslated region


vegetable oil


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Copyright information

© AOCS Press 2006

Authors and Affiliations

  • Douglas R. Tocher
    • 1
  • Xiaozhong Zheng
    • 1
  • Christian Schlechtriem
    • 1
  • Nicola Hastings
    • 1
  • James R. Dick
    • 1
  • Alan J. Teale
    • 1
  1. 1.Institute of AquacultureUniversity of StirlingStirlingScotland, UK

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