Characterization of avian T-cell receptor γ genes

Characterization of avian T-cell receptor γ genes

^*Division of Developmental and Clinical Immunology, Departments of Medicine, Pediatrics, and Microbiology, University of Alabama, and the ^†Howard Hughes Medical Institute, Birmingham, AL 35294; ^‡University of South Florida, All Children’s Hospital, St. Petersburg, FL 33701; ^¶Department of Pathology, Immunology, and Laboratory Medicine, University of Florida College of Medicine, Gainesville, FL 32610; and ^‖Biologie Moléculaire et Cellulaire du Développement, Centre National de la Recherche Scientifique Unité de Recherche Associée 1135, Université Pierre et Marie Curie, 75252 Paris Cedex 05, France

Abstract

In birds and mammals T cells develop along two discrete pathways characterized by expression of either the αβ or the γδ T-cell antigen receptors (TCRs). To gain further insight into the evolutionary significance of the γδ T-cell lineage, the present studies sought to define the chicken TCRγ locus. A splenic cDNA library was screened with two polymerase chain reaction products obtained from genomic DNA using primers for highly conserved regions of TCR and immunoglobulin genes. This strategy yielded cDNA clones with characteristics of mammalian TCR γ chains, including canonical residues considered important for proper folding and stability. Northern blot analysis with the TCRγ cDNA probe revealed 1.9-kb transcripts in the thymus, spleen, and a γδ T-cell line, but not in B or αβ T-cell lines. Three multimember Vγ subfamilies, three Jγ gene segments, and a single constant region Cγ gene were identified in the avian TCRγ locus. Members of each of the three Vγ subfamilies were found to undergo rearrangement in parallel during the first wave of thymocyte development. TCRγ repertoire diversification was initiated on embryonic day 10 by an apparently random pattern of V-Jγ recombination, nuclease activity, and P- and N-nucleotide additions to generate a diverse repertoire of avian TCRγ genes early in ontogeny.