title: Different modes of variation for each BG lineage suggest different functions.
abstract: Mammalian butyrophilins have various important functions, one for lipid binding but others as ligands for co-inhibition of αβ T cells or for stimulation of γδ T cells in the immune system. The chicken BG homologues are dimers, with extracellular immunoglobulin variable (V) domains joined by cysteines in the loop equivalent to complementarity-determining region 1 (CDR1). BG genes are found in three genomic locations: BG0 on chromosome 2, BG1 in the classical MHC (the BF-BL region) and many BG genes in the BG region just outside the MHC. Here, we show that BG0 is virtually monomorphic, suggesting housekeeping function(s) consonant with the ubiquitous tissue distribution. BG1 has allelic polymorphism but minimal sequence diversity, with the few polymorphic residues at the interface of the two V domains, suggesting that BG1 is recognized by receptors in a conserved fashion. Any phenotypic variation should be due to the intracellular region, with differential exon usage between alleles. BG genes in the BG region can generate diversity by exchange of sequence cassettes located in loops equivalent to CDR1 and CDR2, consonant with recognition of many ligands or antigens for immune defence. Unlike the mammalian butyrophilins, there are at least three modes by which BG genes evolve.
authors.affiliation: Department of Pathology, University of Cambridge, Cambridge CB2 1QP, UK.
authors.forename: John
authors.initials: J
authors.lastname: Chattaway
authors.affiliation: Department of Pathology, University of Cambridge, Cambridge CB2 1QP, UK.
authors.forename: R Andrei
authors.initials: RA
authors.lastname: Ramirez-Valdez
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, UK.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Chappell
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, UK.
authors.forename: Joseph J E
authors.initials: JJ
authors.lastname: Caesar
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, UK.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Lea
authors.affiliation: Department of Pathology, University of Cambridge, Cambridge CB2 1QP, UK Department of Veterinary Medicine, University of Cambridge, Cambridge CB3 0ES, UK jfk31@cam.ac.uk.
authors.forename: Jim
authors.identifier: 0000-0002-7216-8422
authors.initials: J
authors.lastname: Kaufman
mesh_terms: D000483:Alleles; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D030161:Avian Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D001483:Base Sequence; D000071797:Butyrophilins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D002645:Chickens; D002875:Chromosomes / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D005091:Exons; D014644:Genetic Variation; D008956:Models, Chemical; D063308:Myelin-Oligodendrocyte Glycoprotein / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D012313:RNA / Q000235:genetics / Q000378:metabolism
chemical_list: D030161:Avian Proteins; D000071797:Butyrophilins; D018076:DNA, Complementary; D063308:Myelin-Oligodendrocyte Glycoprotein; D012313:RNA
keywords: B-G; SKINT; avian; gene conversion; segmental exchange; selection