Characterization of the domestic goat γδ T cell receptor gene loci and gene usage

Goats and cattle diverged 30 million years ago but retain similarities in immune system genes. Here, the caprine T cell receptor (TCR) gene loci and transcription of its genes were examined and compared to cattle. We annotated the TCR loci using an improved genome assembly (ARS1) of a highly homozygous San Clemente goat. This assembly has already proven useful for describing other immune system genes including antibody and leucocyte receptors. Both the TCR gamma (TRG) and TCR delta (TRD) loci were similarly organized in goats as in cattle and the gene sequences were highly conserved. However, the number of genes varied slightly as a result of duplications and differences occurred in mutations resulting in pseudogenes. WC1(+) gamma delta T cells in cattle have been shown to use TCR gamma genes from only one of the six available cassettes. The structure of that C gamma gene product is unique and may be necessary to interact with WC1 for signal transduction following antigen ligation. Using RT-PCR and PacBio sequencing, we observed the same restriction for goat WC1(+) gamma delta T cells. In contrast, caprine WC1(+) and WC1(-) gamma delta T cell populations had a diverse TCR delta gene usage although the propensity for particular gene usage differed between the two cell populations. Noncanonical recombination signal sequences (RSS) largely correlated with restricted expression of TCR gamma and delta genes. Finally, caprine gamma delta T cells were found to incorporate multiple TRD diversity gene sequences in a single transcript, an unusual feature among mammals but also previously observed in cattle.

Automated summary

The study found that goats and cattle share similarities in their T cell receptor genes, particularly in the conserved gene sequences of TCR gamma and TCR delta genes. Despite differences in gene number and specific gene usage, the basic structure is similar.