Characteristics of expression of goose invariant chain gene and comparison of its structure among different species

The invariant chain (Ii) plays a critical role in MHC class II-associated chaperone representing antigen peptide and receptor. In this study, we cloned goose Ii cDNA by 5' and 3' rapid amplification of cDNA ends and tested its mRNA expression in the different tissues by fluorescent quantitative PCR. Two Ii isoforms, GIi-1and GIi-2, were 1,204 and 1,393 bp in length, respectively, and were found in all tested tissues. The expression of GIi in all tested tissues of 2-mo-old geese was higher than in that of embryos and in immune tissues was higher than in other tissues. The comparison of Ii sequences among pigeon, zebra finch, duck, chicken, quail, mouse, human, Pan troglodytes, and Salmo salar in the phylogenetic tree showed that they were classified into 5 lineages. Ii contains 5 functional domains. Further comparison between full-length Ii and each of the 5 domains of 6 species indicated a distinct difference. In 3-dimensional structures some amino acid residues located at critical sites in Ii structural region were identical or similar, which suggests that these residues were important in maintaining Ii essential secondary structures such as β-turn.