The role of γδ T cells in vertebrate immunity is still an unsolved puzzle. Species such as humans and mice display a low percentage of these T lymphocytes (i.e., “γδ low species”) with a restricted diversity of γδ T cell receptors (TR). Conversely, artiodactyl species (i.e., “γδ high species”) ac-count for a high proportion of γδ T cells with large γ and δ chain repertoires. The genomic organisation of the TR γ (TRG) and δ (TRD) loci has been determined in sheep and cattle, noting that a wide number of germline genes that encode for γ and δ chains characterise their genomes. Taking advantage from the current improved version of the genome assembly, we have investigated the genomic structure and gene content of the dromedary TRD locus, which, as in the other mammalian species, is nested within the TR alpha (TRA) genes. The most remarkable finding was the identification of a very limited number of variable germline genes (TRDV) compared to sheep and cattle, which supports our previous expression analyses for which the somatic hypermutation mechanism is able to enlarge and diversify the primary repertoire of dromedary δ chains. Furthermore, the comparison between genomic and expressed sequences reveals that D genes, up to four incorporated in a transcript, greatly contribute to the increased diversity of the dromedary δ chain antigen binding-site.

The domestic pig (Sus scrofa) is a species representative of the Suina, one of the four suborders within Cetartiodactyla. In this paper, we reported our analysis of the pig TRG locus in comparison with the loci of species representative of the Ruminantia, Tylopoda and Cetacea suborders. The pig TRG genomic structure reiterates the peculiarity of the organization of Cetartiodactyla loci in TRGC “cassettes”, each containing the basic V-J-J-C unit. Eighteen genes arranged in four TRGC cassettes, form the pig TRG locus. All the functional TRG genes were expressed, and the TRGV genes preferentially rearrange with the TRGJ genes within their own cassette, which correlates the diversity of the gamma-chain repertoire with the number of cassettes. Among them, the TRGC5, located at the 5’ end of the locus, is the only cassette that retains a marked homology with the corresponding TRGC cassettes of all the analyzed species. The preservation of the TRGC5 cassette for such a long evolutionary time presumes a highly specialized function of its genes, which could be essential for the survival of species. Therefore, the maintenance of this cassette in pigs confirms that it is the most evolutionarily ancient within Cetartiodactyla, and it has undergone a process of duplication to give rise to the other TRGC cassettes in the different artiodactyl species in a lineage-specific manner.

Bottlenose dolphin (Tursiops truncatus) belongs to the Cetartiodactyla and similarly to the other cetaceans represent the most successful mammalian colonization of the aquatic environment. Here we report a genomic, evolutionary and expression study of Tursiops truncatus T cell receptor beta (TRB) genes. Although the organization of the dolphin TRB locus is similar to that of the other artiodactyl species, with three in tandem D-J-C clusters located at its 3’ end, its uniqueness is given by the reduction of the total length due essentially to the absence of duplications and to the deletions that have drastically reduced the number of the germline TRBV genes. We have analyzed the relevant mature transcripts from two subjects. The simultaneous availability of rearranged TRA and TRB cDNA from the peripheral blood of one of the two specimens, and the human/dolphin amino acids multi sequence alignments, allowed us to calculate the most likely interactions at the protein interface between the alpha/beta heterodimer in complex with major histocompatibility class I (MH1) protein. Interacting amino acids located in the CDR-IMGT of the dolphin variable V alpha and beta domains were identified. According to comparative modelisation, the atome pair contact sites analysis between the human MH1 grove (G) domains and the TR V domains confirms conservation of the structure of the dolphin TR/pMH.

In this paper, we report a comprehensive and consistent annotation of the locus encoding the horse T cell receptor b-chain (TRB), as inferred from the most recent genome assembly. The horse TRB locus spans approximately 1 Mb, making it the largest locus among the mammalian species stud-ied to date, with a significantly higher number of genes related to extensive duplicative events. In the region, 136 TRBV, belonging to 29 subgroups, 2 TRBD, 13 TRBJ and 2 TRBC genes, were iden-tified. The general genomic organization resembles that of other mammals, with a V-cluster of 135 TRBV genes, located upstream of two in-tandem aligned TRBD-J-C clusters, and an inverted TRBV gene at the 3’ end of the last TRBC gene. However, the horse b-chain repertoire would be affected by a high number of non-functional TRBV genes. Thus, we queried a transcriptomic da-taset derived from splenic tissue of a healthy adult horse, using each TRBJ gene as a probe to ana-lyse clonotypes encompassing the V(D)J junction. This analysis provided insights into the usage of the TRBV, TRBD and TRBJ genes and the variability of the juxtaposition region. Our results clearly demonstrated that the horse β-chain constitutes a complex level of variability broadly like that described in other mammalian species.