The Effect of Diet and the Masou Salmon Delta5-Desaturase Transgene on Delta6-Desaturase and Stearoyl-CoA Desaturase Gene Expression and N-3 Fatty Acid Level in Common Carp (Cyprinus carpio)
Type of Degreethesis
Fisheries and Allied Aquacultures
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The omega-3 polyunsaturated fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) play important roles in human health. Transgenic technology and diet regulation elevated the omega-3 fatty acid levels in common carp (Cyprinus carpio). Masou salmon Δ5-desaturase-like gene driven by the common carp β-actin promoter (D5D) was transferred into common carp that were later fed two different diets (a formulated diet containing high fatty acid substrates (C18:2n-6/C18:3n-3), high polyunsaturated fatty acid (PUFA) but low highly unsaturated fatty acid (HUFA), and a commercial diet containing low fatty acid substrates, but high PUFA and HUFA to determine its effect on the transcription level of endogenous Δ6-desaturase-like gene (D6D) and stearoyl-CoA desaturase（SCD）in four tissues, muscle, liver, brain and gonad and omega-3 fatty acid content in muscle. The transgene was randomly distributed in all four tissues screened, liver, brain, muscle, and gonad with 8.3%, 10%, 21.7%, and 26.7% of individuals transgenic, respectively, for these 4 tissues. In some cases, the transgene was found in 2 tissues (1.7-5.0%), but no fish were detected that were transgenic in 3 tissues. Quantitative reverse-transcriptase PCR (qRT-PCR) of D6D gene expression in the common carp fed commercial diet tissues showed a rank high to low order of brain, liver, gonad and muscle. And SCD gene expression in the common carp fed commercial diet tissues showed a rank high to low order of liver, brain, gonad and muscle. The D6D and SCD mRNA level were 8.5-fold and 9.1-fold higher in non-transgenic fish liver fed commercial diet than that fed formulated diet, respectively. The SCD mRNA level was 2.2-fold higher in non-transgenic fish muscle fed formulated diet than that fed commercial diet. For the fish fed commercial diet: 1) D6D and SCD mRNA level in muscle of transgenic fish were up-regulated (P<0.05) 12.7-fold and 17.9-fold, respectively, compared to that of non-transgenic fish. 2) D6D mRNA level in the gonad of transgenic fish was up-regulated 6.9-fold (P<0.05) compared to that of non-transgenic fish. 3) In contrast, D6D and SCD mRNA level in the brain of transgenic fish were dramatically down-regulated 50.2-fold and 16.7-fold (P<0.05), respectively, compared to non-transgenic fish. 4) D6D and SCD mRNA level in liver of transgenic fish was down-regulated (P<0.05) 5.4-fold and 2.4-fold, respectively, compared to non-transgenic fish. For the fish fed formulated diet: 1) D6D and SCD mRNA level in muscle of transgenic fish were up-regulated (P<0.05) 41.5-fold and 8.9-fold, respectively, compared to that of non-transgenic fish. 2) D6D and SCD were also up-regulated in liver of transgenic fish, 6.0-fold and 3.3-fold (P<0.05), respectively, compared to non-transgenic fish. 3) In contrast, D6D and SCD mRNA level in the gonad of transgenic fish were down-regulated 5.5-fold (P<0.05) and 12.4-fold (P< 0.05) respectively compared to that of non-transgenic fish. 4) Additionally, D6D and SCD mRNA level in the brain of transgenic fish were down-regulated 14.9-fold and 1.4-fold (P<0.05), respectively, compared to non-transgenic fish. Fatty acid (FA) in the muscle of common carp fed the commercial diet had a higher level of EPA, 1.18-fold (P<0.05), docosapentaenoic acid (DPA) was 1.11-fold (P<0.05) and that of total n-3 was 1.05-fold (P<0.05) than in the muscle of fish fed the formulated diet. The transgenic common carp fed the commercial diet had a 1.07-fold EPA, 1.12-fold DPA, 1.07-fold DHA and a 1.07-fold higher observed total omega-3 fatty acid level than non-transgenic common carp, although these trends were not statistically different (P<0.05). However, this observed trend was not present in fish fed the formulated diet. The results demonstrate that the fatty acid metabolic pathway in fish can be modified by the transgenic technology and diet. The long-term goal is to produce common carp that transmit the Masou Salmon D5D transgene to future generations and optimize the transgene construct and feed formula, leading to commercial application to increase the production of food fish, with elevated omega-3 fatty acids reducing the pressure on natural populations of fish containing these valuable fatty acid profiles and adding value to aquaculture products.