Molecular characterization of MHC class I and beta-2 microglobulin in a clonal strain of ginbuna crucian carp, Carassius auratus langsdorfii

Clonal ginbuna crucian carp is, a naturally gynogenetic fish, and is a useful model animal for studying T-cell-mediated immunity. To gain molecular information on MHC class I molecules from this species, we have identified four types of MHC class I (caauUA-S3n, caauUF-S3n, caauZE-S3n, and caauZB-S3n) and five beta 2-microglobulin (β₂m) (caauβ2m-1a, caauβ2m-1b, caauβ2m-2, caauβ2m-3a and caauβ2m-3b) by an expressed sequence tag (EST) analysis and using homology cloning with degenerated primers. Like UA class I genes in other cyprinid fish, the caauUA-S3n shows features of classical MHC class I, such as conservation of all key amino acids interacting with antigenic peptides, and ubiquitous tissue expression. A phylogenetic analysis shows that the β₂m-1 and β₂m-2 isoforms are clustered with those of other cyprinid fishes, while β₂m-3 isoforms make a cluster that is separated from a common ancestor of salmonid and cyprinid fishes. This finding suggests that the β₂m isoforms of ginbuna cruician carp comprise two lineages and may possess different functions. The MHC class I and β₂m sequences from one clonal strain will facilitate our understanding of the interaction of MHC class I with β₂m in teleosts.