Identification and characterization of T-cell antigen receptor-related genes in phylogenetically diverse vertebrate species.

Characterization of the structure, multiplicity, organization, and cell lineage-specific expression of T-cell receptor (TCR) genes of nonmammalian vertebrate species is central to the understanding of the evolutionary origins of rearranging genes of the vertebrate immune system. We recently described a polymerase chain reaction (PCR) strategy that relies on short sequence similarities shared by nearly all vertebrate TCR and immunoglobulin (Ig) variable (V) regions and have used this approach to isolate a TCR beta (TCRB) homolog from a cartilaginous fish. Using these short PCR products as probes in spleen cDNA and genomic libraries, we were able to isolate a variety of unique TCR and TCR-like genes. Here we report the identification and characterization of a chicken TCR gamma (TCRG) homolog, apparent Xenopus and pufferfish TCR alpha (TCRA) homologs, and two horned shark TCR delta (TCRD)-like genes. In addition, we have identified what could be a novel representative of the Ig gene superfamily in the pufferfish. This method of using short, minimally degenerate PCR primers should speed progress in the phylogenetic investigations of the TCR and related genes and lend important insights into both the origins and functions of these unique gene systems.