Channel catfish (Ictalurus punctatus) protein disulphide isomerase, PDIA6: molecular characterization and expression regulated by bacteria and virus inoculation.

Protein disulfide isomerases (PDIs) are thought to aid protein folding and assembly by catalyzing formation and shuffling of cysteine disulfide bonds in the endoplasmic reticulum (ER). Currently, increasing evidence suggests PDIs play an important role in host cell invasion and they are relevant targets for the host immune response. However the roles of specific PDIs in teleosts are little known. Here, we characterized the Protein disulfide isomerase family A, member 6 (PDIA6) from channel catfish, Ictalurus punctatus (named as ccPDIA6). The catfish ccPDIA6 gene was homologous to those of other vertebrate species with 13 exons and 12 introns. The consensus full-length ccPDIA6 cDNA contained an ORF of 1320 bp encoding a putative protein of 439 amino acids. It had a 19 amino acid signal peptide and two active thioredoxin-like domains. Sequence of phylogenic analysis and multiple alignments showed that ccPDIA6 was conserved throughout vertebrate evolution. Southern blot analysis suggested the presence of one copy of the ccPDIA6 gene in the catfish genome. Tissue distribution shows that ccPDIA6 was expressed in all examined tissues at the mRNA level. When using the aquatic zoonotic pathogens such as Edwardsiella tara, Streptococcus iniae, and channel catfish reovirus （CCRV） to challenge channel catfish, ccPDIA6 expression was significant changed in immune-related tissues such as head kidney, intestine, liver and spleen. The results suggested that ccPDIA6 might play an important role in the immunity of channel catfish. This is the first report that the PDI gene may be involved in fish host defense against pathogen infection.

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