Further characterization of T cell receptor chains of marsupials.

cDNA clones encoding T cell receptor alpha (TCRalpha) and beta (TCRbeta) from the South American opossum, Monodelphis domestica were isolated and characterized. A single clone isolated encoding a TCRalpha chain was full length, containing the complete V (variable), J (joining) and C (constant) regions. Three partial cDNA clones were isolated for TCRbeta which contained complete C sequences. Phylogenetic analysis of the TCR Valpha revealed that the M. domestica sequence and a sequence from the Australian brushtail possum, Trichosurus vulpecula, belong to separate Valpha families and intersperse with sequences from eutherian mammals. Similar to results described for marsupial and eutherian light chains, diversity at the V region of the TCR is ancient and maintained. In contrast phylogenetic analysis of the TCR Calpha and Cbeta sequences from M. domestica, T. vulpecula, and other vertebrates revealed that the marsupial TCR C grouped together forming a sister group to eutherian mammals.

Cloning of marsupial T cell receptor alpha and beta constant region cDNAs.

Partial cDNAs encoding the tammar wallaby (Macropus eugenii) T cell receptor alpha constant region (TCRalphaC) and T cell receptor beta constant region (TCRbetaC) 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 TCRalphaC and TCRbetaC. 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 TCRalphaC sequences, with 55.9% identity at the amino acid level. For TCRbetaC, the T. vulpecula and human beta1 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, TCRalphaC and TCRbetaC homologues from eutherian mammals, consistent with the current views of both mammalian and TCR evolution.