Characterization of five caspase genes and their transcriptional changes in response to exogenous iridescent virus challenge in the whiteleg shrimp (Litopenaeus vannamei)

Abstract

As one of the most important enzyme families, the caspase family works effectively in immunization reactions, and many of its members mediate programmed cell death and pathogen immunity through complicated molecular pathways. However, studies on the genes of caspase family is very limited in invertebrates. In this work, we examined their nucleotide sequences, three-dimensional structures, molecular evolution, and potential functions in the world-famous whiteleg shrimp (Litopenaeus vannamei) in a systematic manner. The deduced protein sequences were revealed to have a potential active site (QACRG pentapeptide), which seems to be conserved in most caspases. However, protein conserved domains and three-dimensional structures present notable variances, implying that these caspase proteins may play various roles in invertebrates and vertebrates. Conserved domain prediction and phylogenetic analysis of multiple species suggest that caspase-3 may be an intermediate transitional form of caspase genes during the evolution from invertebrates to vertebrates. The up-regulation of caspase-1, -2, -3 transcripts in the hepatopancreas tissue of whiteleg shrimp after iridescent virus infection implies that these proteins are involved in the immune response to the virus. Our transcriptome data also support in-depth understanding of the molecular evolution, as well as the physiological roles of the caspase family in the whiteleg shrimp when this invertebrate species was infected by exogenous viral pathogens.