Characterisation of T cell antigen receptor α chain isotypes in the common carp

T cell receptor α (TCRα) chain has been characterised in several teleost species to date. Here, a reverse transcription-polymerase chain reaction (RT-PCR) strategy was used to isolate cDNA clones encoding TCRα chain from an individual of the common carp (Cyprinus carpio.L.). The Vα sequences identified were most similar to Vα of other teleosts, and could be classified into as many as 14 Vα families. For the Jα sequences, diversity comparable to that seen in other teleosts could be identified, and the J-region motif was well conserved. The Cα sequences demonstrated the highest similarity to zebrafish Cα and possessed a well-conserved transmembrane (TM) region. Two Cα isotypes with a complete C region were obtained, designated Cα1 and Cα2, with ∼70% similarity at the amino acid level (∼85% identity at the nucleotide level), and, in addition, Cα2 contained two unique sequences, designated Cα2a and Cα2b, with 93% similarity (96% identity). Therefore, the results obtained using an individual clearly showed that carp possesses at least two Cα loci, possibly as a result of tetraploidisation.