cDNA cloning and genomic structure of the duck (Anas platyrhynchos) MHC class I gene

In order to provide data for studies on disease resistance, duck MHC class I cDNA (Anpl-MHC I) was cloned from a duck cDNA library and the genome structure was investigated. Anpl-MHC I genes encoded 344-355 amino acids. The genomic organization is composed of eight exons and seven introns. Based on the genetic distance, Anpl-MHC I cDNA from six individuals can be classified into four lineages (from Anpl-UAA to Anpl-UDA). A total of 28 amino acid positions in the peptide-binding domain (PBD) showed high scores by Wu-kabat index analysis. The Anpl-MHC amino acid sequence displayed seven critical HLA-A2amino acids that bind with antigen polypeptides, and have an 83.6-88.5% amino acid homology with each lineage, a 55.2-64.6% amino-acid homology with chicken MHC class I (B-FIV21, B-FIV2, Rfp-Y), and a 40.3-42.8% homology with mammalian MHC class I. Nested PCR detected that Anpl-MHC I can be expressed in the brain, heart, kidney, intestines and bursa. Compared with the human HLA-A2 tertiary structure of the PBD, Anpl-MHC I had an insertion or deletion variation in four domains (A-D). The phlyogenetic tree appears to branch in an order consistent with accepted evolutionary pathways.