Taurine Transporter Gene Expression Of Grouper(Epinephelus Coioides) After Dietary Taurine Administration

Grouper(Epinephelus) is a kind of seafood fish with high economic value.The aquaculture of grouper has formed a large scale in the southeast coastal area of China Fujian,Guangdong,and Hainan.However,the low application level of grouper feed does still not match the rapid development of grouper aquaculture section.Taurine transporter(TauT)is the key carrier in the transmembrane transport of taurine,and plays an important role in the growth,metabolism,and sexual maturity of fish.In this study,we have isolated a cDNA encoding the TauT mRNA from grouper(Epinephelus coioides)liver and determined the TauT mRNA expression in tissues after dietary taurine administration.The results are presented as follows:1.TauT gene cloning of grouperThe full length of TauT coding sequence from liver of grouper was isolated.The protein sequence of TauT has 1881 bp and encodes 626 amino acids with a molecular weight of 70126.80 Da.It contains 12 transmembrane regions.There is a ring of hydrophilic group linking the third and the fourth transmembrane region.From homology analysis and phylogenetic analysis,Japanese sea bass is closest to grouper,followed by Atlantic salmon and tilapia.The phylogenetic relationship of other freshwater fish such as carp and zebra fish is far more distant with grouper.2.Tissue expression analysisThe TauT mRNA expression levels in tissues of grouper were determined.TauT mRNA was expressed in all the tested tissues and the levels of TauT mRNA were different in various tissues.The highest expression levels of TauT mRNA were found in liver,heart and brain,followed by kidney,gills and spleen.The lowest mRNA levels occurred for gut,muscle and adipose tissues.3.Effect of dietary taurine level on the growth performance in grouperAn 84-day feeding trial was conducted to determine the effects of dietary taurine on the growth performance in grouper.The fish were sampled at 28 th day,56 th day and84 th day.The weight gain rate in taurine-treated group was significantly higher than the control group(p<0.05),and was significantly higher in group fed 1% taurine dietthan the other groups(p<0.05).The taurine concentrations in liver,muscle and intestinal tract increased with both age and dietary taurine level,and taurine concentrations in taurine-treated groups were significantly higher than that in control group(p<0.05).4.Effect of dietary taurine administration on the expression of TauT mRNA in grouperAt day 28,the TauT mRNA level of grouper reached a peak at 1% dietary taurine level,and the value was significant higher than that in groups fed the basal diet and 0.5% taurine diet(p<0.05).There was a similar tendency of TauT mRNA level when fish were sampled at day 56 and day 84.The TauT mRNA level was decreased with the increase in duration of feeding period,which was in accordance with the requirement of taurine in grouper,whereas was oppose to the concentration of taurine of tissues.