Co-evolution with chicken class I genes.
The concept of co-evolution (or co-adaptation) has a long history, but application at molecular levels (e.g., 'supergenes' in genetics) is more recent, with a consensus definition still developing. One interesting example is the chicken major histocompatibility complex (MHC). In contrast to typical mammals that have many class I and class I-like genes, only two classical class I genes, two CD1 genes and some non-classical Rfp-Y genes are known in chicken, and all are found on the microchromosome that bears the MHC. Rarity of recombination between the closely linked and polymorphic genes encoding classical class I and TAPs allows co-evolution, leading to a single dominantly expressed class I molecule in each MHC haplotype, with strong functional consequences in terms of resistance to infectious pathogens. Chicken tapasin is highly polymorphic, but co-evolution with TAP and class I genes remains unclear. T-cell receptors, natural killer (NK) cell receptors, and CD8 co-receptor genes are found on non-MHC chromosomes, with some evidence for co-evolution of surface residues and number of genes along the avian and mammalian lineages. Over even longer periods, co-evolution has been invoked to explain how the adaptive immune system of jawed vertebrates arose from closely linked receptor, ligand, and antigen-processing genes in the primordial MHC.
Department of Pathology, University of Cambridge, Cambridge, UK.|Department of Veterinary Medicine, University of Cambridge, Cambridge, UK.
Jim
J
Kaufman
D000818:Animals; D030161:Avian Proteins / Q000235:genetics / Q000276:immunology*; D002645:Chickens / Q000235:genetics / Q000276:immunology*; D019143:Evolution, Molecular; D005805:Genes, MHC Class I / Q000235:genetics / Q000276:immunology*; D006239:Haplotypes; D006801:Humans; D008957:Models, Genetic; D018448:Models, Immunological; D011110:Polymorphism, Genetic / Q000235:genetics / Q000276:immunology*
D030161:Avian Proteins
T-cell receptors; avian; evolution; major histocompatibility complex