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-κB 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.