Molecular characterization reveals involvement of four caspases in the antibacterial immunity of tongue sole (Cynoglossus semilaevis)

• CsCas1, CsCas2, CsCas3, and CsCas9 have conserved caspase domain and catalytic site.
• The four caspases share 35.4%–76.2% sequence identities with known fish caspases.
• The four caspases were expressed in a wide range of tissues in varying levels.
• Bacterial infection altered caspase expression in a time/tissue-dependent manner.
• Overexpression of the four caspases in tongue sole reduced bacterial infection.

Caspases are a family of proteases involved in many important biological processes including apoptosis and inflammation. In this study, we analyzed in a comparative manner the expression patterns and immune effects of four different types of caspases, i.e. caspase-1 (CsCas1), caspase-2 (CsCas2), caspase-3 (CsCas3), and caspase-9 (CsCas9), from the teleost fish tongue sole (Cynoglossus semilaevis). CsCas1, CsCas2, CsCas3, and CsCas9 share 35.4%–58.5%, 61.2%–75.3%, 52.3%–65.6%, and 63.0%–76.2% overall sequence identities, respectively, with their counterparts in teleost species. CsCas1, CsCas2, CsCas3, and CsCas9 possess the caspase domain and catalytic site conserved in known caspases. The expressions of the four caspases were detected in a wide range of tissues, however, the expression levels varied between different tissues and caspases. Following bacterial infection, the expressions of the four caspases were upregulated or downregulated to significant extents in a time- and tissue-dependent manner. In vivo analysis showed that overexpression of each of the caspases in tongue sole significantly enhanced the ability of the fish to resist bacterial dissemination in and colonization of tissues. These results indicate an involvement of fish caspases in bacteria-induced immune response and demonstrate for the first time that caspase-1, 2, 3, and 9 are essential to the optimal defense against bacterial infection in fish.