Identification and characterization of caspase-7 in pufferfish (Takifugu obscurus) in response to bacterial infection and cell apoptosis

Caspase-7 is a key effector caspase that takes part in apoptosis, inflammation, and in immune responses in mammals. To date, studies on the expression and functional characterization of caspase-7 upon apoptosis in teleosts are limited. Here, we identify a caspase-7 homolog (pfcasp-7) from pufferfish (Takifugu obscurus) and characterize its expression pattern during bacterial challenge. The open reading frame of pfcasp-7 is 942 base pairs in length, encoding a polypeptide of 313 amino acids. The deduced amino acid sequence is highly homologous to other known caspase-7 s, which contain a carboxyl-terminal catalytic domain and a pentapeptide active-site motif ((192)QACRG(196)). Quantitative real-time qPCR analysis indicated that pfcasp-7 is expressed in all examined tissues (kidney, blood, gills, gut, heart, spleen, liver, brain, and muscle), with the highest expression in the kidney ( > 117-fold higher than the lowest expression in muscle), followed by expression in the blood and gills. Challenging with Aeromonas hydrophila induced apoptosis in the blood and kidney and resulted in the significant upregulation of pfcasp-7 expression, which was consistent with the detection of apoptosis by flow cytometry. Pfcasp-7 expression was also upregulated in the kidney leukocytes following in vitro stimulation with lipopolysaccharide and inactivated A. hydrophila. Taken together, these results suggest that pfcasp-7 is involved in apoptosis in pufferfish after bacterial infection.