Functional adaptive diversity of the Atlantic salmon T-cell receptor gamma locus

The Atlantic salmon (Salmo salar) T-cell receptor γ (TCRγ) gene has extensive diversity in its capacity for antigen recognition due to the V–J–C gene segments recombinational possibilities, and N-region diversity. This is the first report completely characterizing and annotating a TCRγ gene locus in teleosts. We identified two different TCRγ loci in Atlantic salmon. The first locus, TCRγ 1, spans 260 kbp and contains four tandemly repeated clusters each of which consists of 1–4 variable (V) segments, 1–2 sets of a joining (J) segment and a constant (C) region. In total, 10 V segments, 5 J segments and 5 C regions were found in locus 1. In the second locus, TCRγ 2, a single non-expressed V–J–C cluster was found. Surprisingly, the Atlantic salmon TCRγ loci have a larger number of C regions relative to other teleosts, mouse and human. In addition, each Atlantic salmon TCRγ C region has a different connecting peptide region that may result in distinct cellular responses. Expression data confirm the diverse repertoire found at the genomic level. At least 6 out of 7 functional V segments, all 5 J segments and all 5 C regions found in TCRγ 1 were identified in TCRγ transcription analysis. The identification and characterization of the functional TCRγ 1 along with the associated TCR α/δ locus suggest that Atlantic salmon have a functional γδ T-cell immune component.