Divergent T-cell receptor delta chains from marsupials.

Area of Science:

• Immunogenetics
• Comparative Genomics
• Evolutionary Biology

Background:

• T-cell receptor delta (TRD) genes are crucial for adaptive immunity.
• Previous studies suggested limited TRD diversity in marsupials.
• Understanding TRD evolution across mammalian groups is important.

Purpose of the Study:

• To investigate the T-cell receptor delta (TRD) gene repertoire in marsupials.
• To determine the evolutionary relationship of marsupial TRD genes with those of other mammals.
• To analyze the expression patterns of TRD variable (TRDV) and constant (TRDC) segments in marsupials.

Main Methods:

• Sequencing of expressed sequence tags (ESTs) from a thymus cDNA library of Isoodon macrourus.
• Identification and analysis of TRD genes within the whole genome sequence of Monodelphis domestica.
• Comparative analysis of TRD sequences from Isoodon macrourus, Macropus eugenii, and Monodelphis domestica.

Main Results:

• All three studied marsupial species possess multiple, highly divergent TRD loci, contrasting with eutherian mammals.
• Marsupial TRD sequences cluster into two distinct groups: one related to eutherian TRD genes, and a marsupial-specific clade.
• Specific associations between TRDV and TRDC segments were observed, correlating with their evolutionary origins (eutherian-like or marsupial-specific).

Conclusions:

• Marsupials exhibit a unique genomic organization of TRD loci compared to eutherian mammals.
• The presence of multiple TRD loci has shaped the evolution and diversification of TRD genes in marsupials.
• Distinct expression patterns of TRDV-TRDC combinations reflect the evolutionary history of these gene segments in marsupials.