Calcineurin subunit B is involved in shell regeneration in Haliotis diversicolor.

Abalone shells are mainly composed of two major polymorphs of CaCO3 that are distributed in different layers of the shell. The process of shell biomineralization is controlled by genes and proteins expressed within the mantle epithelium. In this present paper, we conducted a shell regeneration experiment to study the role of HcCNA and HcCNB (individual subunits of calcineurin) in shell biomineralization in H. diversicolor. The results of qPCR showed that HcCNB is upregulated to a greater extent than HcCNA in the mantle after shell notching. In vivo study of the effects of rHcCNB injection showed a significantly higher percentage of regenerated shell length, but not area, in the injected group compared to the control group. In addition, SEM observation of the inner surface of the regenerated shells revealed three different zones including prismatic, nacreous, and a distinct transition zone. Changes in the crystal organization and ultrastructure are clearly evident in these three zones, particularly after 3 weeks of rHcCNB administration. We hypothesize that this is due to faster biomineralization rates in the rHcCNB treated group. Taken together, our results demonstrate that HcCNB participates in shell regeneration in H. diversicolor. As calcineurin subunits have also been implicated in shell formation in bivalves, these findings suggest that calcineurin subunits may play important roles in biomineralization in all conchiferans.

Characterization of calcineurin A and B genes in the abalone, Haliotis diversicolor, and their immune response role during bacterial infection.

Calcineurin (CN) is known to be involved in many biological processes, particularly, the immune response mechanism in many invertebrates. In this study, we characterized both HcCNA and HcCNB genes in Haliotis diversicolor, documented their expression in many tissues, and discerned their function as immune responsive genes against Vibrio parahaemolyticus infection. Similar to other mollusk CNs, the HcCNA gene lacked a proline-rich domain and comprised only one isoform of its catalytic unit, in contrast to CNs found in mammals. HcCNB was highly conserved in both sequence and domain architecture. Quantitative PCR and in situ hybridization revealed that the genes were broadly expressed and were not restricted to tissues traditionally associated with immune function. Upon infection of H. diversicolor with V. parahaemolyticus (a bacteria that causes serious disease in crustaceans and mollusks), both HcCNA and HcCNB genes were highly up-regulated at the early phase of bacterial infection. HcCNB was expressed significantly higher than HcCNA in response to bacterial challenge, suggesting its independent or more rapid response to bacterial infection. Together, the two CN genes are unique in their gene structure (particular HcCNA) and distribution in mollusk species and likely function as immune responsive genes along with many other genes that are enhanced in the early phase of V. parahaemolyticus infection in abalone.