Porcine T-cell receptor β-chain: A genomic sequence covering Dβ1.1 to Cβ2 gene segments and the diversity of cDNA expressed in piglets including novel alternative splicing products

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Porcine TCRβ-chain cDNA clones were isolated from thymic and peripheral blood lymphocytes of piglets. Using these nucleotide sequences, a genomic 18 kbp sequence stretch covering Dβ1 to Cβ2 gene segments was identified, which revealed that the porcine TCRβ-chain locus consists of two sets of Dβ-Jβ-Cβ gene groups with each set having a Dβ gene segment, seven Jβ gene segments and a down stream Cβ gene segment composed of four exons. This structure is consistent with other known mammalian TCRβ-chain loci. With this genomic information, TCRβ-chain clones from cDNA libraries were analyzed. Sixteen Vβ gene segments were obtained accompanied by either Dβ1 or Dβ2 and by one of the nine Jβ gene segments. Five different Cβ cDNA sequences were obtained including four types of Cβ1 sequences and one type of Cβ2 sequence. The differences among the Cβ1 sequences are either allelic polymorphisms or two splice variants, one being a product of exon1 splicing to exon3 (exon2 skipping), and another being an alternative splicing using a splice acceptor site newly discovered inside Cβ1 exon4. The latter splice acceptor site was also found in human, mouse and horse all giving short cytoplasmic domain with Phe at their C-terminal ends. Other splicing products included trans-splicing of Jβ2 to Cβ1, non-functional splicing of two Jβ gene segments in tandem and a part of Jβ2.7-Cβ2 intron to Cβ2 exon1. Numerous examples of splice variants may suggest the involvement of splicing in generating TCRβ-chain functional diversity.