Molecular cloning, characterization and expression profiles of Annexin family (ANXA1~A6) in yellow catfish (Pelteobagrus fulvidraco) and ANX regulation by CpG ODN responding to bacterial infection

Up to now, many previous reports have emphasized that Annexins (ANX) family played an important role in immune responses. Aeromonas hydrophila (A. hydrophila), the most common zoonotic pathogenic bacteria of yellow catfish (Pelteobagrus fulvidraco), can cause serious economic loss, especially to yellow catfish with high economic value. In our previous work, we demonstrated that synthetic oligodeoxynucleotides containing CpG motifs (CpG ODN) owned powerful immunostimulatory activity. However, the relationship among Pelteobagrus fulvidraco Annexins (Pf_ANX), CpG ODN and A. hydrophila is unknown. Therefore, we cloned Pf_ANX1-6 genes and analyzed its sequences, structures, genetic evolution, post-translation modifications (PTMs), Ca2+ ion binding sites and tissue distribution to reveal the relevance. In addition, we investigated the responses of ANXA1-6 and cytokines in intestine and spleen as well as morbidity/survival rate of fish post CpG ODN immunization and/or A. hydrophila infection. The results showed that compared with challenge alone (challenge-CK) group, the CpG immunization following challenge (CpG-challenge) group displayed relatively flat IL-1β level throughout in both organs. Meanwhile, the expression of IFN-γ and morbidity/survival rate of fish in CpG-challenge group showed a great improvement compared with the challenge-CK group. Our results indicated that CpG ODN could improve morbidity/survival by up-regulating Pf_ANXA 1, 2 and 5 in the intestine and spleen to ameliorate inflammatory responses and promote anti-infective responses. Our findings offer some important insights into ANX related to the immunity of fish infection and lay a theoretical basis for the prevention and treatment of fish infections.