CHARACTERIZATION OF AVIAN T-CELL RECEPTOR-GAMMA GENES

In birds and mammals T cells develop along two discrete pathways chara cterized by expression of either the alpha beta or the gamma delta T-c ell antigen receptors (TCRs). To gain further insight into the evoluti onary significance of the gamma delta T-cell lineage, the present stud ies sought to define the chicken TCR gamma locus. A splenic cDNA libra ry was screened with two polymerase chain reaction products obtained f rom genomic DNA using primers for highly conserved regions of TCR and immunoglobulin genes. This strategy yielded cDNA clones with character istics of mammalian TCR gamma chains, including canonical residues con sidered important for proper folding and stability. Northern blot anal ysis with the TCR gamma cDNA probe revealed 1.9-kb transcripts in the thymus, spleen, and a gamma delta T-cell line, but not in B or alpha b eta T-cell lines. Three multimember V gamma subfamilies, three J gamma gene segments, and a single constant region C gamma gene were identif ied in the avian TCR gamma locus. Members of each of the three V gamma subfamilies were found to undergo rearrangement in parallel during th e first wave of thymocyte development. TCR gamma repertoire diversific ation was initiated on embryonic day 10 by an apparently random patter n of V-J gamma recombination, nuclease activity, and P- and N-nucleoti de additions to generate a diverse repertoire of avian TCR gamma genes early in ontogeny.