Cloning and expression analysis of two carbonic anhydrase genes in white shrimp Litopenaeus vannamei, induced by pH and salinity stresses

Carbonic anhydrase catalyzes the interconversion of CO2 and HCO3−, and plays important role in keeping balance of body acid base and regulating the pH of body fluid. In this study, the full-length cDNAs encoding CAc (cytoplasmic carbonic anydrase) and CAg (glycosyl-phosphatidylinositol-linked carbonic anhydrase) from Litopenaeus Vannamei were isolated by RACE-PCR (GenBank accession no. HM991703.2 and JX975725). LvCAc is consituted by an ORF of 810 bp encoding for a protein of 29.56 kDa. The LvCAg is constituted by an ORF of 927 bp encoding for a protein of 32.6 kDa. The comparison of the deduced amino acid sequences with CAc and CAg from other crustaceans showed high conservation of the residues and domains essential to the function of these two enzymes. LvCAc mRNA expression was detected in gills, muscle, hepatopancreas, and hemocytes, and LvCAg mRNA expression was found in gills, muscle, and hepatopancreas. Using real-time quantitative PCR, we investigated two kinds of CA gene expression changes of L. vannamei challenged with different salinities and pH. Following salinity and pH treatment, LvCAc expression increased in 24-48 h, reaching the highest level at 24 h, and restored to intial level at 72 h after the challenge of salinity change; while CAg expression presented peak change in 24-48 h, reaching the highest level at 48 h after the challenge of salinity decrease. Both of them were higher than that in the control group. The CAc and CAg expressions increased in 48 h and 12 h respectively after the challenge of pH increases or decreases, and there was no significant difference in the expression compared to the control group in other testing time.