Characterization and expression of gamma-interferon-inducible lysosomal thiol reductase (GILT) gene in amphioxus Branchiostoma belcheri with implications for GILT in innate immune response

An amphioxus cDNA, AmphiGILT, encoding GILT protein was isolated from the gut cDNA library of Branchiostoma belcheri. It codes for a deduced protein of 254 amino acids, which has all the main features typical of GILT proteins including the signature sequence CQHGX2CX2NX4C, CXXC motif and 11 conserved cysteines. Phylogenetic analysis showed that AmphiGILT and sea urchin GILT clubbed together and positioned at the base of vertebrate GILT clade, suggesting that both AmphiGILT and sea urchin GILT might share some characteristics of the archetype of vertebrate GILT proteins. The genomic DNA sequence of B. floridae contains seven exons and six introns, which is similar to vertebrate GILT exon-intron organization. AmphiGILT was expressed in a tissue-specific manner with the most abundant mRNA in the digestive system including hepatic caecum and hind-gut. It was also found that mammalian IFN-γ only exerted a slight effect on the expression of GILT gene in amphioxus, forming a contrast to the marked induction of human and mouse GILT expression by IFN-γ. Taken the absence of the adaptive immune system including MHC class II molecules and lymphocytes into consideration, these results suggest that AmphiGILT is highly likely to play a role in the innate immune responses in amphioxus.