| Due to the changes of nutrition,psychology and environment,weaned piglets will experience stress response.Weaning stress will cause reduced feed and nutrient intake,diarrhea and subsequently slower or retarded growth in piglets.Additionally,stress response of weaned piglets also leads to changes in certain gene expression in piglets.DNA methylation is an important way of gene expression control.The modification is mainly mediated by DNA methyltransferases(DNMTs).DNMT2 belongs to the DNA methyltransferase family,while its DNA methylation function has been controversial.It was reported to mainly methylate C38 of various tRNAs,to generate 5-methyl cytidine(m5C).tRNA methylation by DNMT2 was shown to enhance tRNA stability,to prevent tRNA cleavage under stress condition,and to ensure accuracy of peptide synthesis.DNMT2 was also reported to be involved in RNA processing under cellular stress,cellular defense mechanism against viral infection.Recently,DNMT2 was suggested to regulate the expression of heat shock protein and to improve the tolerance to NO stress in Entamoeba histolyca.These data implies a possible link between DNMT2 and weaning stress of piglets.In order to elaborate whether DNMT2 is associated weaning stress of piglets,18 healthy castrated Yorkshire piglets(6～7 kg)with similar genetic background were randomly divided into 6 groups,each group with 3 piglets.The piglets were sacrificed at 1d before weaning(age 20 days),1d,3d,5d,7d and 14d after weaning(age 22,24,26,28 and 35 days,respectively.Porcine brain,heart,liver,spleen,lung,kidney,stomach,duodenum,jejunum,ileum tissue and blood were collected right after the slaughter procedures.Serum biochemical indicators were examined,and the morphological changes of various organ sections were observed.In addition,DNMT2 expression was monitored by RT-PCR and western blot analysis.Finally,DNMT2 overexpression model was established in mice and performed in weaned piglets to test the impact of DNMT2 over-expression on daily weight gain of weaned piglets.The results are as follows:1.The serum biochemical indexes:While serum ALP dropped slightly,serum UA,GLU,ALB levels decreased significantly(P<0.05)after weaning compared to those 1d before weaning.Interestingly,TP,LDH,ALT,and AST increased,yet not significantly.2.HE staining and DNMT2 immunostaining of piglet liver and kidney sections:After weaning,weaned piglets exhibited ballooning degeneration and fatty degeneration in hepatocellular,fatty degeneration in renal tubule cells.DNMT2 was enriched in the degenerating cells in liver and kidney as well as nearby area.3.DNMT2 expression in weaned piglets:By DNMT2 expression was examined by RT-PCR and Western blot before and after weaning,the results revealed decreased expression of DNMT2 in kidney,stomach,duodenum and jejunumafter weaning.4.DNMT2 overexpression model in mice:pcDNA3.1-DNMT2 was injected to mice,this led to increased level of mRNA and protein levels for DNMT2 as compared with the PBS control group5.Impact of DNMT2 overexpression on daily weight gain of weaned piglets:pcDNA3.1-DNMT2 recombinant plasmid ws injected to weaned piglets with PBS as control.The results showed that overexpression of DNMT2 steadily promotes daily weight gain of weaned piglets,with 3 folder higher than that for PBS group(P<0.05).Conclusions:1.Weaning stress caused changes in the serum biochemical indexes of piglets.In addition,ballooning and fatty degeneration were observed in hepatocells,while fatty degeneration occurred in renal tubular cells.2.DNMT2 was enriched in and around degenerative cells.3.Weaning stress led to decreased expression of DNMT2 in kidney andgastrointestines of piglets.4.DNMT2 overexpression could overcome the harmful effect of weaning stress and promote growth performance of weaned piglets.Meaning:This study provides basis of molecular level for weaning stress,and provides theoretical basis which develop enzymic preparations against weaning stress. |
