Identification and characterization of caspases genes in rainbow trout (Oncorhynchus mykiss) and their expression profiles after Aeromonas salmonicida and Vibrio anguillarum infection

Caspases are highly conserved cysteine-dependent aspartyl-specific proteases that play an important role in regulating cell death and inflammation. However, the caspase genes have not been systematically studied in rainbow trout (Oncorhynchus mykiss). Rainbow trout experienced 4 rounds (4R) of genome duplication in the evolutionary history. Thereby an increased numbers of paralogs are observed in trout, probably with more complicated gene functions. We identified 18 caspase genes in rainbow trout, including two inflammatory caspases (casp1a, casp1b), six apoptosis executioner caspases (casp3, casp3a1, casp3a2, casp3b, casp6, and casp7), nine apoptosis initiator caspases (casp2a, casp2b, casp8, casp9a, casp9b, casp10a, casp10b, casp20a, and casp20b) and one uncategorized caspase gene (casp17). To investigate the potentially physiological functions of caspase genes, we challenged the rainbow trout with Aeromonas salmonicida (A. salmonicida) and Vibrio anguillarum (V. anguillarum). Results showed that the CASP3-regulated intrinsic apoptosis was activated after A. salmonicida infection, while the CASP8 and CASP6-regulated extrinsic apoptosis exerted the greatest effect on trout challenged with V. anguillarum. In response to V. anguillarum infection, the data of RNA-Seq further showed the casp8 was tightly integrated with the significantly enriched Gene Ontology terms and functional pathways, including apoptosis regulation, pathogen detection and immunomodulation. Our study provides a foundation for the physiological functions and regulatory network of the caspase genes in teleosts.