Expression analysis of Acanthopagrus schlegelii PRL1 and PRL2 in response to acute salinity stress

【Objective】To understand the expression patterns of prolactin genes（PRL1 and PRL2）in different tissues and under different salinity stresses，so as to provide a reference for the determination of the optimal salinity range in the breeding process of Acanthopagrus schlegelii.【Method】PRL1 and PRL2 genes of A. schlegelii were amplified by RTPCR，and bioinformatics analysis was performed by ExPASy，NetNGlyc，Swiss-Model and other online softwares. The expression of PRL1 and PRL2 genes in different tissues and under different salinity stresses was detected by real-time fluorescence quantitative PCR.【Result】The full length of PRL1 open reading frame（ORF）was 639 bp，encoding 212 amino acids with a molecular weight of 23.32 kD and an isoelectric point（pI）of 6.70；and the ORF of PRL2 gene was 750 bp， encoding 249 amino acids with a molecular weight of 28.31 kD and pI of 8.37. PRL1 and PRL2 proteins were both composed of a signal peptide domain and a Hormone 1 domain. In the secondary structure of PRL1 protein，69.34% of α-helix and 30.66% of random curl were found，including 1 glycosylation site and 37 phosphorylation sites. In the secondary structure of PRL2 protein，α-helix accounted for 67.07% and random curl accounted for 32.93%，including 1 glycosylation site and 21 phosphorylation sites. The results of tissue expression analysis showed that PRL1 and PRL2 genes were expressed in all 12 tested tissues. The highest expression levels of PRL1 and PRL2 were both detected in brain，significantly higher than the relative expression levels in other tissues（P<0.05，the same below）. In the 5‰ salinity treatment group，PRL1 gene was significantly up-regulated at 4 h under salt stress，PRL2 gene was extremely significantly up-regulated at 8 h under stress（P<0.01）. Both of them reached peak value at 24 h，then began to decline slowly，and their expression levels were still significantly higher than those of the control group at 72 h of stress. The expression levels of PRL1 and PRL2 genes in the 25‰ and 35‰ salinity treatment groups were significantly lower than those in the control group after 72 h stress.【Conclusion】Low salinity stress can promote the expression of PRL1 and PRL2 genes，while high salinity stress can inhibit the expression of PRL1 and PRL2 genes. In other words，A. schlegelii PRL1 and PRL2 genes play important regulatory roles in the adaptation to fresh water.