title: Two ancient allelic lineages at the single classical class I locus in the Xenopus MHC.
abstract: Unlike all other vertebrates examined to date, there is only one detectable class I locus in the Xenopus MHC. On the bases of a nearly ubiquitous and high tissue expression, extensive polymorphism, and MHC linkage, this gene is of the classical or class Ia type. Sequencing analysis of class Ia cDNAs encoded by eight defined MHC haplotypes reveals two very old allelic lineages that perhaps emerged when humans and mice diverged from a common ancestor up to 100 million years ago. The unprecedented age of these lineages suggests that different class Ia genes from ancestors of the laboratory model Xenopus laevis are now expressed as alleles in this species. The lineages are best defined by their cytoplasmic and alpha2 peptide-binding domains, and there are highly diverse alleles (defined by the alpha1 peptide-binding domain) in each lineage. Surprisingly, the alpha3 domains are homogenized in both lineages, suggesting that interallelic gene conversion/recombination maintains the high sequence similarity.
authors.affiliation: Department of Microbiology and Immunology, University of Miami School of Medicine, FL 33136, USA. mflaj001@umaryland.edu
authors.forename: M F
authors.initials: MF
authors.lastname: Flajnik
authors.forename: Y
authors.initials: Y
authors.lastname: Ohta
authors.forename: A S
authors.initials: AS
authors.lastname: Greenberg
authors.forename: L
authors.initials: L
authors.lastname: Salter-Cid
authors.forename: A
authors.initials: A
authors.lastname: Carrizosa
authors.forename: L
authors.initials: L
authors.lastname: Du Pasquier
authors.forename: M
authors.initials: M
authors.lastname: Kasahara
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D017124:Conserved Sequence; D019143:Evolution, Molecular; D005805:Genes, MHC Class I; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D010802:Phylogeny; D011894:Rana pipiens / Q000235:genetics / Q000276:immunology; D017422:Sequence Analysis, DNA; D014982:Xenopus laevis / Q000235:genetics* / Q000276:immunology*
chemical_list: D015395:Histocompatibility Antigens Class I