title: The dominantly expressed class I molecule of the chicken MHC is explained by coevolution with the polymorphic peptide transporter (TAP) genes.
abstract: In most mammals, the MHC class I molecules are polymorphic and determine the specificity of peptide presentation, whereas the transporter associated with antigen presentation (TAP) heterodimers are functionally monomorphic. In chickens, there are two classical class I genes but only one is expressed at a high level, which can result in strong MHC associations with resistance to particular infectious pathogens. However, the basis for having a single dominantly expressed class I molecule has been unclear. Here we report TAP1 and TAP2 sequences from 16 chicken lines, and show that both genes have high allelic polymorphism and moderate sequence diversity, with variation in positions expected for peptide binding. We analyze peptide translocation in two MHC haplotypes, showing that chicken TAPs specify translocation at three peptide positions, matching the peptide motif of the single dominantly expressed class I molecule. These results show that coevolution between class I and TAP genes can explain the presence of a single dominantly expressed class I molecule in common chicken MHC haplotypes. Moreover, such coevolution in the primordial MHC may have been responsible for the appearance of the antigen presentation pathways at the birth of the adaptive immune system.
authors.affiliation: Institute for Animal Health, Compton RG20 7NN, United Kingdom.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Walker
authors.forename: Lawrence G
authors.initials: LG
authors.lastname: Hunt
authors.forename: Anna K
authors.initials: AK
authors.lastname: Sowa
authors.forename: Karsten
authors.initials: K
authors.lastname: Skjødt
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Göbel
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Lehner
authors.forename: Jim
authors.initials: J
authors.lastname: Kaufman
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000818:Animals; D017951:Antigen Presentation / Q000235:genetics; D002645:Chickens / Q000235:genetics*; D019143:Evolution, Molecular; D015395:Histocompatibility Antigens Class I / Q000235:genetics*; D008969:Molecular Sequence Data; D021381:Protein Transport
chemical_list: D018528:ATP-Binding Cassette Transporters; D015395:Histocompatibility Antigens Class I; C477327:transporter associated with antigen processing (TAP)