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

T cell receptor alpha (TCRalpha) 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 TCRalpha chain from an individual of the common carp (Cyprinus carpio.L.). The Valpha sequences identified were most similar to Valpha of other teleosts, and could be classified into as many as 14 Valpha families. For the Jalpha sequences, diversity comparable to that seen in other teleosts could be identified, and the J-region motif was well conserved. The Calpha sequences demonstrated the highest similarity to zebrafish Calpha and possessed a well-conserved transmembrane (TM) region. Two Calpha isotypes with a complete C region were obtained, designated Calpha1 and Calpha2, with approximately 70% similarity at the amino acid level ( approximately 85% identity at the nucleotide level), and, in addition, Calpha2 contained two unique sequences, designated Calpha2a and Calpha2b, with 93% similarity (96% identity). Therefore, the results obtained using an individual clearly showed that carp possesses at least two Calpha loci, possibly as a result of tetraploidisation.