Ig and T cell receptor (TCR) genes consist of separate genomic elements, which must undergo rearrangement and joining before a functional protein can be expressed. Considerable plasticity in the genomic arrangement of these elements has occurred during the evolution of the immune system. In tetrapods, all Ig and TCR chain elements are arranged as translocons. In teleosts, the Ig heavy and TCR chains are translocons, but light chain genes may occur as clusters. However, in chondrichthyes, all of the Ig light and heavy chain genes are arranged as clusters. These clusters vary in number from <10 to several hundred, depending on isotype and species. Here, we report that the germ-line gene for the TCR γ chain in a chondrichthyan, the sandbar shark (Carcharhinus plumbeus), is present as a single locus arranged in a classic translocon pattern. Thus, the shark utilizes 2 types of genomic arrangements, the unique cluster organization for Ig genes and the "conventional" translocon organization for TCR genes. The TCR γ translocon contains at least 5 V region genes, 3 J segment genes, and 1 C segment. As expected, the third hypervariable segment (CDR3), formed by the rearrangement of the Vγ and Jγ segments, contributed the major variability in the intact V region structure. Our data also suggest that diversity may be generated by mutation in the V regions.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - May 26 2009|
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