cDNA cloning and polymorphic domains of the major histocompatibility complex (MHC) class Iα in two Chinese native chicken breeds

Major histocompatibility complex (MHC) is a highly polymorphic gene and plays an important role in immune system for vertebrate. To understand the polymorphism character of domestic, we cloned 32 cDNAs of MHC class I alpha genes of two local chicken breeds in different areas of China. There were 112 variable amino acid residues in all five domains (leader peptide, alpha 1, alpha 2, alpha 3 and TM/CY domains) of the putative alpha chain, and 76 of them were located in alpha 1 and alpha 2 domains. There were 23 to 25 polymorphic sites with high mutation frequency in alpha 1 and alpha 2 domains. Comparison of chicken with duck, human and mouse revealed that the two domains were highly similar among different species, and some highly polymorphic sites were located at the sites 9, 111(114), 113 (116) and 153 (156). Analysis of the phylogenetic tree indicated no relationship between the breeds and polymorphic alleles. All these results therefore indicate that MHC I class molecule of domestic chickens was more influenced by the pressure of common pathogens rather than geographic differences.