Differential gene expression of Gymnocypris przewalskii under saline-alkali stress

Saline-alkali water areas are widely distributed in China,but the utilization ratio is very low.High salinity and high carbonate alkalinity are considered to be the major stressors for aquatic animals living in saline-alkali waters.Gymnocypris przewalskii,scale-less carp,is an important economic fish in Qinghai Lake,the largest inland lake in China,which has a low concentration of dissolved oxygen,strong alkalinity and high salinity.The saline-alkali tolerance of G.przewalskii is very high.The study is to determine genome-wide gene expression profiles and to better understand how saline-alkali stress influences gene expression in G.przewalskii.Suppression subtractive hybridization method was applied to construct directional cDNA libraries and to obtain differential expression genes.450 positive clones from libraries were randomly selected to validate with PCR,and 318 clones showed a single channel result.The results showed that the quality of libraries were perfect.Consequently,195 positive clones were selected for analysis through Blast.Altogether 91 genes were identified from the forward and reverse libraries,69 of them were well annotated.These differentially expressed genes could be divided into a number of biological gene ontology groups related to catalytic activity,binding,cell,immune system process,transporter activity,structural molecule activity,cellular process,development,reproduction,biological regulation.Catalytic activity,binding and cell genes were up-regulated,while immune system process genes were down-regulated.Quantitative real-time PCR showed that the expression of Na+,K+-ATPase β1b subunit and glutamine synthase increased significantly at 72h after exposure.Compared with the control group,the expression of Na+,K+-ATPase β1b subunit increased 5.6 fold,glutamine synthase increased 2.3 fold.High saline-alkali water could change the osmotic pressure and acid-base balance in fish,injure surface mucous membrane of gill and kidney,and inhibit the immune system to a certain extent.Therefore,G.przewalskii may activate and enhance partial signal path to activate the metabolism,transporter and tolerance of gene expression.G.przewalskii improved the expression and activity of catalyticase to increase the ion exchange with the environment and maintain osmotic equilibrium;raised the expression of glutamine synthase to increase the content of glutamine and serum urea nitrogen,thus rebuilt the acid-base balance;synthetized heat shock protein and annexin to increase the defense ability,thus reduced stress response.