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

The Atlantic salmon (Salmo salar) T-cell receptor gamma (TCRgamma) 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 TCRgamma gene locus in teleosts. We identified two different TCRgamma loci in Atlantic salmon. The first locus, TCRgamma 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, TCRgamma 2, a single non-expressed V-J-C cluster was found. Surprisingly, the Atlantic salmon TCRgamma loci have a larger number of C regions relative to other teleosts, mouse and human. In addition, each Atlantic salmon TCRgamma 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 TCRgamma 1 were identified in TCRgamma transcription analysis. The identification and characterization of the functional TCRgamma 1 along with the associated TCR alpha/delta locus suggest that Atlantic salmon have a functional gammadelta T-cell immune component.