IDENTIFICATION OF T-CELL RECEPTOR ALPHA-CHAIN GENES IN THE CHICKEN

T-cell receptor (TCR) alpha-chain (TCRalpha) and beta-chain (TCRbeta) genes are well characterized in mammals, while only TCRbeta genes have been identified in other vertebrates. To identify avian TCRalpha genes, we used monoclonal anti-CD3 antibodies to isolate chicken TCRalpha for peptide sequence analysis. Degenerate oligonucleotide probes were then used to isolate a candidate TCRalpha cDNA clone that hybridized with a 1.7-kb mRNA species present only in alphabeta T cells and in tissues populated by these cells. Southern blot analysis revealed gene rearrangement in thymocytes and alphabeta T-cell lines. The TCRalpha cDNA candidate encoded an open reading frame of 275 amino acids, the predicted variable (V)-, joining (J)-, and constant (C)-region amino acid sequences of which shared almost-equal-to 40%, 60%, and 25% homology with corresponding mammalian sequences. A single C. gene and almost-equal-to 25 V(alpha) genes were identified by using region-specific probes. The V(alpha) cDNA probe isolated from a V(beta)1+ cell line reacted with transcripts from one of five V(beta)2+ cell lines, suggesting shared use of V(alpha) genes by V(beta)1+ and V(beta)2+ T cells and the existence of other V(alpha) gene families. A genomic V(alpha) sequence was flanked by classical recombination signal sequences but, unlike previously defined V genes, the leader and V(alpha) region were encoded by a single exon. The data indicate evolutionary conservation of the basic TCRalpha gene structure in birds and mammals.