Molecular cloning and polymorphism of major histocompatibility complex class I genes from grass carp (Ctenophayngodon idellus)

In order to clarify the molecular sequences, allelic polymorphism and the tertiary structure of grass carp (Ctenophayngodon idellus) MHC class I, and to further study their relationship with disease resistances, grass carp MHC class I gene (Ctid-MHC I) was cloned from a cDNA library and the allelic polymorphism in the population was investigated. The results showed that most of the variations exist in the peptide-binding domain (PBD) and high polymorphism was identified in the Ctid-MHC I allelic genes from 12 individuals. Based on the genetic distance, Ctid-MHC class I can be classified into 6 types (from Ctid-MHC I-UA to Ctid-MHC I-UF) which were subdivided into 9 lineages (from A to I). Comparison of the Ctid-MHC I among animals and humans showed that the key amino acids of the peptide binding sites are conserved. Analysis of the tertiary structure of the PBD between Grass carp and human crystallographic data of HLA-A2, the variation with insertion or deletion was found in eight regions (A similar to H). The phylogenetic tree of MHC class I indicates the evolution of MHC class I among grass carp, fish, amphibian, birds, higher vertebrates and humans.