Abstract
T lymphocytes are the principal actors of vertebrates’ cell-mediated immunity. Like B cells, they can recognize an unlimited number of foreign molecules through their antigen-specific heterodimer receptors (TRs), which consist of αβ or γδ chains. The diversity of the TRs is mainly due to the unique organization of the genes encoding the α, β, γ, and δ chains. For each chain, multi-gene families are arranged in a TR locus, and their expression is guaranteed by the somatic recombination process. A great plasticity of the gene organization within the TR loci exists among species. Marked structural differences affect the TR γ (TRG) locus. The recent sequencing of multiple whole genome provides an opportunity to examine the TR gene repertoire in a systematic and consistent fashion. In this review, we report the most recent findings on the genomic organization of TRG loci in mammalian species in order to show differences and similarities. The comparison revealed remarkable diversification of both the genomic organization and gene repertoire across species, but also unexpected evolutionary conservation, which highlights the important role of the T cells in the immune response.
Highlights
T lymphocytes play a crucial role in the immune surveillance of all jawed vertebrates
On the basis of the accepted phylogeny, we describe the genomic characteristic of the TRG locus in Cetartiodactyla/Carnivora lineages, with respect to Rodentia/Lagomorpha/Primata
In the sandbar shark (Carcharhinus plumbeus), a cartilaginous fish, the TRG locus consists of a single J-C gene cluster preceded by five TRGV genes
Summary
T lymphocytes play a crucial role in the immune surveillance of all jawed vertebrates. Γδ T cells are a functionally heterogeneous population, details of their functions are becoming clearer They recognize antigens directly and without processing, in a manner similar to immunoglobulins (IG) [9], or presented by RPI-MH1Like proteins [10], providing more flexible and not yet clear recognition of a wide range of ligands (soluble, membrane-bound, and unprocessed antigens). The number of V, D, and J genes in the germline DNA, and the somatic V-(D)-J rearrangement mechanism unique to the adaptive immune response, contribute to the huge diversity of the expressed TR repertoire, allowing potentially billions of different TR antigen-binding sites to be produced from a limited set of genes [2]. From the TRB and TRA/TRD loci, the TRG locus shows great gene-organization plasticity related to the evolution of different species. For a comparative analysis, the genomic organization of the TRG locus in other vertebrate species, outgroups respective to placental mammals, is described
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