Effects Of Different Dietary Carbohydrate Levels And Nutritional Status On Activities And Expression Of Glucose Metabolism Key Enzymes Gene In Different Fish Species

This experiment was conducted to determine the effect of different dietary carbohydrate levels and different nutritional status on activity and expression of glucose metabolism key enzymes gene GK,PK and PEPCK in three marine fishes of different food habits.The omnivorous tilapia(Oreochromis niloticus 31.5±0.29 g),moderate carnivorous golden pompano(Trachinotus ovatus 85.17±1.89g)and ferocious carnivorous cobia(Rachycentron canadum 23.33±0.29 g),were taken as the research objects.Dextrin was used as the main dietary carbohydrate source,diets with three carbohydrate levels(low dextrin LD,middle dextrin MD and high dextrin HD)and three nutritional status(starvation S,refeeding R,continuous feed C)to attain the same nitrogen level,respectively.Each species randomly selected 60 juvenile fishes with physical uniform were feeding experimental period of 8 weeks.The results are as follows:1.Cloning and sequence analysis of GK,PK and PEPCKThe full-length c DNA of GK,PK and PEPCK in pompano and GK,PK in cobia were obtained using 5?-RACE and 3?-RACE.These five genes: Pompano gk containing 1437 bp open reading frame(ORF).KM262819 containing 1593 bp ORF.KJ438292 containing1875 bp ORF.Cobia gk containing 1599 bp.KM262818 containing 1599 bp ORF.The conclusion of three genes(GK,PK and PEPCK)in these three kinds of fishes with different food habits: there are the same food habits having closer relations in homology and evolutionary was found in this study.2.Effects of different dietary carbohydrate levels and different nutritional status on expression and activities of GK in different fish speciesWith the increase of dietary carbohydrate levels,the expression of GK in liver of tilapia,pompano and cobia increased significantly(P<0.05),the activities of GK in liver of tilapia,pompano and cobia did not make significant difference(P<0.05).In the same carbohydrate level,cobia's GK m RNA level is higher than pompano and tilapia,tilapia's GK activites is higher than pompano,and pompano is higher than cobia.On different nutritional status,the three fishes GK m RNA levels are all show that: S and R group lower than C group(P<0.05),GK activities have no significant differences except cobia gets high in C group.On the same nutritional status,the GK gene expression of tilapia and pompano in S and R groups are significantly higher than that in cobia(P<0.05),the GKactivities of tilapia and pompano in S and R groups are significantly higher than that in cobia(P<0.05).3.Effects of different dietary carbohydrate levels and different nutritional status on expression and activities of PK in different fish speciesWith the increase of dietary carbohydrate levels,the expression of PK in liver of tilapia,pompano and cobia increased significantly(P<0.05),but no significant difference was found between the activities of tilapia,pompano and cobia(P>0.05).In the parallel carbohydrate level,compared with pompano and cobia,tilapia's PK expression significantly increased(P<0.05),no differences,however,was obvioused between the two carnivorous fishes(P>0.05).compared with cobia,PK activities of tilapia and pompano significantly increased in LD and MD group(P<0.05).Three fishes PK m RNA levels were all higher in R and C group(P<0.05)with different nutritional status.There were not significant differences in PK activities of S and R group in the three fishes(P>0.05).On the same nutritional status,the PK gene expression of cobia was higher than pompano,but no difference between cobia and tilapia(P>0.05).The PK m RNA expression levels of the two carnivorous fishes were leveled off in continued feeding group,but both significantly lower than tilapia(P<0.05).The PK activities of cobia was lower than pompano and tilapia,and no difference was found between pompano and tilapia(P>0.05).The PK activities in C group showed: pompano>tilapia>cobia.4.Effects of different dietary carbohydrate levels and different nutritional status on expression and activities of PEPCK in different fish speciesThe PEPCK m RNA levels decreased with the increasing of dietary carbohydrate level(P<0.05).PEPCK activity were decreased,the HD group PEPCK activity of the three fishes were significantly decreased by 24.78%,28.05% and 26.03% than the LD group(P<0.05),respectively.In the same carbohydrate level,Ferocious carnivorous cobia' genetic express ion of PEPCK is significantly higher than moderate carnivorous golden pompano,and pompano is higher than omnivorous tilapia.All treatments show higher PEPCK activities in tilapia than cobia significantly.however tilapia and pompano obvious no differences(P<0.05).On different nutritional status,genetic expression of PEPCK in S group is higher than R group(P<0.05),and R group' is higher than C group(P<0.05).On the same nutritional status,the levels of PEPCK m RNA in those three group,cobia is the highest in three fishes.The activities of PEPCK makes no difference in cobia(P<0.05),but S group of pompano showed 1.25-fold significantly higher than C group,wherever tilapia' result showed Sgroup is higher than R group(P<0.05),and R group' is higher than C group(P<0.05).On the same nutritional status,PEPCK activities in all three treatmeats(S,R and C)demonstrated tilapia>pompano>cobia.The results showed that gluconeogenic capacity might be responsible for food habits,the PEPCK enzyme activity and gene expression of three fish were significantly inhibited with increasing of dietary dextrin levels,the degree of inhibition of m RNA expression was varied from food habits,the inhibition extent of Tilapia was the highest and Cobia subject to a minimum degree of inhibition.