| Food intake of fish is closely related to aquaculture and its economic benefits.Mandarin fish（Siniperca chuatsi）,as an economic species,has a special food habit and eats live prey fish instead of dead prey fish or artificial diet when was born.Histone modification,as an epigenetic regulation mechanism,can regulate gene transcription.This study was to explore the role of histone methylation modification in mandarin fish domestication and high-carbohydrate diet intake,which provided a theoretical basis for mandarin fish domestication and the food intake decrease after high-carbohydrate diet intake in carnivorous fish.It is of great significance for mandarin fish domestication and the development of artificial diet.In the research 1:mandarin fish were domesticated to feed on artificial diets for three processes.In first process,the fish were fed with live pery fish（Cirrhinus mrigala）for 3 days,starved for 2 days,and fed with artificial diet for 1 day.For the fish did not eat artificial diets,the process above was continued for twice,and for the fish ate artificial diets in first process,in second process the fish were fed with live prey fish for 1 day and artificial feed for 3 days,then the fish ate artificial feed were selected,in third process,the process in second processwas continued.finally,two groups of fish were obtained,which did not eat or ate artificial feed in the three domestication processes,named hard domesticated group（W）and easily domesticated group X,respectively.Transcriptome analysis showed that there were 54 differentially expressed genes in X group and W group.Compared with the X group,29 genes were up-regulated and 25 genes were down regulated in the W group,in which the most differentially expressed genes in pathways was metabolic pathway,in which there were 10,6 and 13differentially expressed genes in lipid metabolism,signal transduction and global and overview maps,respectively.The common pathways of differential metabolites and genes were glycerin lipid metabolism and unsaturated fatty acid biosynthesis pathway and retinol metabolism.The metabolomics results showed in positive mode,44 and 20ions were identified at MS1 and MS2 levels,while in negative mode,24 and 11 ions were identified at MS1 and MS2 levels.EZH1 gene expression were significantly decreased,the protein level of H3K27me3 were significantly decreased,the total DNA methylation level of TFⅡF gene was significantly increased,and TFⅡF gene expression increased in group X.This reason why mandarin fish in group A can feed on artificial diet stably might be decreased gen expression of EZH1,leading to the decreased level of H3K27me3,followed by the increased of TFIIF gene methylation.Up-regulation of TFIIF gene expression might increase the gene expression in glycerophosphate metabolism pathway,glycerophosphate metabolism and retinol metabolism.This study elucidates the mechanism of aritificial diet domestication from the perspective of epigenetic modification,which has important guiding significance for aritificial diet domestication in fish.In the research 2:the mandarin fish were domesticated to feed on carbohydrate-rich diets（16.16%）,after 61 days of feeding,several fish fed on artificial diet well during the whole feeding period,named Group A;the other fish fed on artificial diet well at the beginning,but the food intake decreased to 1/2（anorexia）,even did not eat artificial diets for 5 days,named Group B.Using transcriptome sequencing,we investigated the differentially expressed genes between Group A and B,S6k,glut1/2,tnfα,,traf2,creb,socs3,ins-r,pepck,fbp and jak was up-regulated;irs1 and pi3k were down-regulated in the mandarin fish of Group B.The m TOR and Jak/STAT pathways were activated in the mandarin fish with anorexia,which was consistent with the higher expression levels of pepck gene.Using RT-PCR and WB,the higher expression of histone methyltransferase SETD1B gene and the increased level of H3K4me3（histone H3 tri-methylated at lysine 4）were was found in the fish of Group B.Chromatin immunoprecipitation results showed that the H3K4me3 was enriched in the pepck gene promoter,and the higher enrichment of H3K4me3 in pepck promoter of the liver in fish of group B.In addition,at the cellular level,the SETD1B inhibitor chaetocin was used at 3×10-5to treat hepatocyte for 17h,the level of H3K4me3 and pepck gene expeession were down-regulated after treatment,the results showed SETD1B regulates H3K4me3 to activate the expression of pepck,resulting in disturbance of glucose metabolism.That is the reason for anorexia of mandarin fish in group B.The study shows the mechanism of anorexia after feed on carbohydrate enriched diets from the perspective of epigenetic modification,which is of great significance to the research and development of carbohydrate enriched artificial diets and the development of industry for mandarin fish. |
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