Identification, structural characterization and expression analysis of a novel carbonic anhydrase from freshwater mussel Hyriopsis cumingii

In this study, an α-carbonic anhydrase (α-CA), HcCA3, from Hyriopsis cumingii was characterized. The full-length cDNA of HcCA3 was 1628 bp, including a CA domain and an ORF of 1053 bp which encoded 350 amino acids. Its predicted molecular weight was 39.69 kDa and the pI was 5.92. qRT-PCR was used to determine the expression of the gene in various tissues at 0 h, 3 h, 6 h, 12 h, 24 h, 48 h, 96 h, 7 d, 14 d, 21 d, 28 d and 35 d after inserting the pearl nucleus. The results showed that the HcCA3 was highly expressed in the mantle, whereas its expression was low in other tissues. Expression in the posterior mantle pallial (pMP) was significantly higher than that in the anterior mantle pallial (aMP) and mantle center (MC). Expression in the aMP, pMP and MC was significantly higher in purple mussels compared with that in white mussels. At the same time, during the formation of pearls, expression in the aMP, pMP and pearl sac (PS) decreased and then increased; whereas expression in the MC increased and then decreased. In-situ hybridization showed that the HcCA3 was expressed in both inside and outside epidermal cells. In protein level, Western blot showed that HcCA3 was mainly expressed in the aMP, pMP and MC. Our results suggest that HcCA3 play a role in the formation of shell and pearl sac formation.