Oyster studies reveal the duplication and functional diversification of Bivalvia caspase-8 genes

Caspase-8, first classified as a pro-apoptotic caspase, is considered to have arisen from duplication with caspase-10 and involves multiple immune and inflammatory responses in mammals. However, few are known on the phylogeny and function of caspase-8 in molluscs, one of the largest phyla in marine invertebrates. In this study, we conducted phylogenetic and functional analysis on molluscan caspase-8-like genes. Results indicate that duplication occurred in molluscan caspase-8-like genes, resulting in at least two caspase-8 copies in some groups of bivalves. Additional studies in Pacific oyster Crassostrea gigas showed different spatio-temporal expression patterns and subcellular localizations of CgCaspase-8-1 and CgCaspase-8-2. While no interaction was observed between CgCaspase-8-2 and CgFADD, the adaptor molecule in apoptosis, yeast two-hybrid and co-immunoprecipitation assays suggested the interaction between CgCaspase-8-1 and CgFADD, indicating its pro-apoptotic function. In addition, CgCaspase-8-1 showed interaction with the CARD domain of CgRIG-I. Together with two NF-& kappa;B subunits (Cgp105 and CgRel), their transcripts were up-regulated in response to poly(I:C) stimuli, supporting the immune function of both pro, and anti-inflammation. The results provide insight into the evolution and functional diversification of Bivalvia caspase-8 genes.