Genomic characterization and sequence diversity of the β2-microglobulin gene in the miiuy croaker, Miichthys miiuy.

β2-Microglobulin (β2m) is related to major histocompatibility complex class I alpha chains, and forms cell-surface glycoproteins that mediate a variety of functions in immune defense. In general, β2m has no isoforms and is not polymorphic in higher vertebrates, but polymorphisms between different alleles have been found in some fish species. In this study, full-length β2m cDNA and genomic sequences were cloned from the miiuy croaker (Miichthys miiuy). The miiuy croaker β2m gene shares many of the same characteristics as other fish species. Three exons and two introns were identified in the miiuy croaker β2m gene; these genomic structural features are similar to those present in other fish. The deduced β2m amino acid sequence exhibited 34.7-90.1% identity with mammal and teleost β2m amino acid sequences. Sequence polymorphism analysis in six individuals identified three alleles that encoded two proteins, confirming that β2m polymorphisms exist in this species. Phylogenetic analysis elucidated the evolutionary history of the β2m protein among warm-blooded vertebrates and bony fish.