title: Different evolutionary histories of the two classical class I genes BF1 and BF2 illustrate drift and selection within the stable MHC haplotypes of chickens.
abstract: Compared with the MHC of typical mammals, the chicken MHC (BF/BL region) of the B12 haplotype is smaller, simpler, and rearranged, with two classical class I genes of which only one is highly expressed. In this study, we describe the development of long-distance PCR to amplify some or all of each class I gene separately, allowing us to make the following points. First, six other haplotypes have the same genomic organization as B12, with a poorly expressed (minor) BF1 gene between DMB2 and TAP2 and a well-expressed (major) BF2 gene between TAP2 and C4. Second, the expression of the BF1 gene is crippled in three different ways in these haplotypes: enhancer A deletion (B12, B19), enhancer A divergence and transcription start site deletion (B2, B4, B21), and insertion/rearrangement leading to pseudogenes (B14, B15). Third, the three kinds of alterations in the BF1 gene correspond to dendrograms of the BF1 and poorly expressed class II B (BLB1) genes reflecting mostly neutral changes, while the dendrograms of the BF2 and well-expressed class II (BLB2) genes each have completely different topologies reflecting selection. The common pattern for the poorly expressed genes reflects the fact the BF/BL region undergoes little recombination and allows us to propose a pattern of descent for these chicken MHC haplotypes from a common ancestor. Taken together, these data explain how stable MHC haplotypes predominantly express a single class I molecule, which in turn leads to striking associations of the chicken MHC with resistance to infectious pathogens and response to vaccines.
authors: Institute for Animal Health, Compton, Berkshire, United Kingdom.
authors: Iain
authors: I
authors: Shaw
authors: Timothy J
authors: TJ
authors: Powell
authors: Denise A
authors: DA
authors: Marston
authors: Ken
authors: K
authors: Baker
authors: Andrew
authors: A
authors: van Hateren
authors: Patricia
authors: P
authors: Riegert
authors: Michael V
authors: MV
authors: Wiles
authors: Sarah
authors: S
authors: Milne
authors: Stephan
authors: S
authors: Beck
authors: Jim
authors: J
authors: Kaufman
mesh_terms: D000818:Animals; D001483:Base Sequence; D002645:Chickens / Q000235:genetics* / Q000276:immunology; D019143:Evolution, Molecular; D015870:Gene Expression; D005805:Genes, MHC Class I; D040961:Genetic Drift; D006239:Haplotypes; D015395:Histocompatibility Antigens Class I / Q000145:classification* / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D011401:Promoter Regions, Genetic
chemical_list: D015395:Histocompatibility Antigens Class I