Structural and comparative analysis of the T cell receptor gamma (TRG) locus in Oryctolagus cuniculus.

In mammals, T cells develop along two discrete pathways characterized by expression of either the αβ or the γδT cell receptors. Human, mouse, and dog display a low peripheral blood γδ T cell percentage, while sheep accounts for a high proportion of γδ T lymphocytes. In all these species, the genomic organization of the T cell receptor gamma (TRG) locus is well known. To gain further insight into the evolutionary significance of the γδ T cell lineage, the present study has defined the genomic organization of the TRG locus in rabbit (Oryctolagus cuniculus), another mammalian γδ high species, as deduced from the genome assembly. The rabbit TRG locus spans about 70 kb and consists of ten TRGV, two TRGJ genes, and one TRGC gene located 5' to 3' in the locus. When we compared the rabbit sequence with the human, mouse, sheep, and dog counterparts, a higher identity with human as well as sheep with respect to mouse and dog was evident, providing that in the different mammalian species, the TRG locus appears to have evolved independently without any correlation with the γδ condition. The complete sequence of the rabbit TRG locus described here provides also a resource for supporting functional studies especially in the context of the γδ T cell function.