Evolutionary history of the T cell receptor complex as revealed by small-spotted catshark (Scyliorhinus canicula)

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In every jawed vertebrate species studied so far, the T cell receptor (TCR) complex is composed of two different TCR chains (α/β or γ/δ) and a number of CD3 subunits responsible for transmitting signals into the T cell. In this study, we characterised all of the TCR and CD3 genes of small-spotted catshark (Scyliorhinus canicula) and analysed their expression in a broad range of tissues. While the TCR complex is highly conserved across jawed vertebrates, we identified a number of differences in catshark, most notably the presence of two copies of both TCRβ and CD3γδ, and the absence of a functionally-important proline rich region from CD3ε. We also demonstrate that TCRβ has duplicated independently multiple times in jawed vertebrate evolution, bringing additional diversity to the TCR complex. This study reveals new insights about the evolutionary history of the TCR complex and raises new avenues for future exploration.HighlightsWe describe the first cloning of all CD3 subunits from a cartilaginous fish.The core TCR complex has been highly conserved during vertebrate evolution.Cartilaginous fish have multiple copies of CD3γδ and the TCRβ constant region.The TCRβ constant region is copy number variable across jawed vertebrate phylogeny.Unexpectedly, the proline rich region is absent from small-spotted catshark CD3ε.

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