Variability in an MHCMosa class II beta chain-encoding gene in striped bass (Morone saxatilis)

The major histocompatibility complex (MHC) class II B locus of the striped bass (Morone saxatilis) was found to contain multiple forms of the class II B gene. Seven complete MHC class II B cDNA clones were isolated and sequenced, identifying five unique allelic forms of a MHC class II B gene. Among three specimens, each representing a geographically distinct population (Chesapeake Bay, MD; Roanoke River, NC; and Santee-Cooper Reservoir, SC) extensive variability was detected in the beta 1 encoding domain, which corresponds with the functional peptide-binding region (PBR) of known MHC class II molecules. The location of variable amino acid residues in the beta 1 domains corresponds with polymorphic sites observed in other teleosts and higher vertebrates. The amino acid translated beta 2 domain encoding regions, transmembrane regions, and cytoplasmic regions of the five clones correlated well with those of known vertebrate MHC class II proteins. Seventy-one percent of the variability found within the presumed PBR encoded at the MHCMosa class II B locus corresponded with that of the PBR of a human MHC class II B gene. Overall, the Mosa sequences showed greatest similarity to the MHC class II B genes of cichlid fishes, as expected from phylogenetic relationships.