Cloning Of â–³6 Fatty Acid Desaturase (â–³6fad) And The Effect Of Different Dietary Lipids On Growth, Fatty Acid Composition And â–³6fad Mrna Relative Expression Level Of Juvenile Abalone (haliotis Discus Hannai Ino.)

A series of experiments were carried out to investigate the effects of dietary different lipids on growth, fatty acid composition of abalone (Haliotis discus hannai Ino.).Results showed that abalone have the ability to synthesyze HUFA from C18 substrates. Base on it, experiments on how the vegetable oil and fish oil affected this biosynthesis capability have been investigated and△6FAD gene which is crucial in HUFA biosynthesis was cloned from abalone using molecular techniques. The effect of different dietary lipids on△6FAD mRNA relative expression level was researched in hepatopancreas and muscle of juvenile abalone.The experimental results were as follows:1,A 120 day-feeding experiment was conducted to investigate the effect of dietary different lipids on survival, growth and fatty acid composition in hepatopancreas and muscle of abalone (Haliotis discus hannai Ino.).(initial weight: (0.38±0.01)g; initial shell length:(15.06±0.21)mm) in circulated rearing system. Olive oil (OO), Grape seed oil (GO), Linseed oil (LO), EPA oil (EO) and ARA oil (AO) (3.5% dry weight) were respectively used as different lipid sources to formulate five different purified diets in this experiment. Different kinds of lipid sources significantly affected the growth of juvenile abalone (P<0.05).The weight growth rate (WGR) of abalone fed the diet with OO grew the best among all the treatments. There was no significant difference between that of AO and EO groups, both of which grew worse than OO group. The WGR of abalone fed diets contained GO(enriched with only C18:2n-6) and LO(enriched with only C18:3n-3) were significantly lower than those of OO, AO and EO groups. The differences in DISL of all the treatments were similar with WGR (P<0.05).The fatty acid composition in hepatopancreas and muscle of abalone was found to be correlated with dietary fatty acid composition. The analysis of fatty acid in hepatopancreas of juvenile abalone fed with GO and 00 as lipid source respectively indicated that abalone have the ability to convert C18:2n-6 to ARA, and C18:3n-3 to EPA. However, the bioconversion capacity from EPA to DHA was limited in abalone.2,Cloning ofΔ6FAD in hepatopancreas of abalone and the effect of different lipids in diets onΔ6FAD mRNA relative expression in hepatopancreas and muscle were studied in this section. A6FAD cDNA was cloned in juvenile abalone by 3'RACE and 5'RACE technology. The full length of the abalone A6FAD cDNA was 1525bp which included an open reading frame(ORF) of 1320bp and specified a protein of 439 amino acids which exhibited high amino acid identity with vertebrateΔ6FAD (>49%).The protein contained three histidine-rich regions (combined with a di-iron to make the catalyzed center of enzyme);a conserved heme-binding domain (HPGG) of cytochrome b5;membrane-spanning domains made by long hydrophobic domains, which are characteristics ofΔ6FAD.Fish oil full of HUFA (AO and EO) significantly suppressed theΔ6FAD mRNA relative expression in hepatopancreas of juvenile abalone compared with vegetable oil (00) enriched with C18 unsaturated fatty acid by real-time quantitative PCR (RT-PCR) (P<0.05). However GO significantly enhanced theΔ6FAD mRNA relative expression in muscle of juvenile abalone (P<0.05).This research for the first time demonstrated that abalone has the bioconversion capacity to biosynthesize HUFA using C18:2n-6 and C18:3n-3 as substrates and this capacity can be affected by different dietary lipids.Δ6FAD mRNA relative expression can be enhanced by C18PUFA existed in vegetable oil which contribute to stimulating HUFA biosynthesis.