Cloning of marsupial T cell receptor α and β constant region cDNAs

Partial cDNAs encoding the tammar wallaby (Macropus eugenii) T cell receptor alpha constant region (TCRαC) and T cell receptor beta constant region (TCRβC) were obtained using reverse transcriptase-coupled polymerase chain reaction (RT-PCR). These PCR products were used to screen a brushtail possum (Trichosurus vulpecula) lymph node cDNA library, resulting in the isolation of clones containing the complete coding regions for TCRαC and TCRβC. These constitute the first marsupial T cell receptor sequences to have been elucidated. Sequence analysis of the T. vulpecula constant region revealed a considerable level of sequence identity with TCR of other species, particularly eutherian mammals, at both the nucleic acid and amino acid levels. At the nucleotide level, 65.8% sequence identity was calculated for the T. vulpecula and human TCRαC sequences, with 55.9% identity at the amino acid level. For TCRβC, the T. vulpecula and human β1 sequence identity at the nucleotide level was 75.1% and at the amino acid level, 67.0%. Phylogenetic analyses based on the T. vulpecula sequences indicated that these sequences are basal to, but also most closely related with, TCRαC and TCRβC homologues from eutherian mammals, consistent with the current views of both mammalian and TCR evolution.