T-cell antigen receptors in Atlantic cod (Gadus morhua L.): structure, organisation and expression of TCR alpha and beta genes

By using short degenerate primers complementing conserved T-cell antigen re ceptor (TCR) variable and constant region segments for PCR, we were able to isolate putative TCR alpha and beta chain full length cDNAs in Atlantic co d. The Ver and VP domains have the canonical features of known teleost and mammalian TCR V domains, including conserved residues in the beginning of F R2 and at the end of FR3. The J alpha and J beta region possess the conserv ed Phe-GIy-X-Gly motif found in nearly all TCR and immunoglobulin light cha in J regions. Similar to other vertebrates, the Atlantic cod Ca: and C beta sequences exhibit distinct immunoglobulin, connecting peptide, transmembra ne and cytoplasmic regions. The Atlantic cod C beta sequence lacks a cystei ne in its connecting peptide region, but other motifs proposed to be import ant for dimerisation and cell surface expression are observed. Four differe nt cod C beta sequences were identified, two of which share 3' untranslated regions different from one of the other two sequences, suggesting the exis tence of isotypic gene variants of C beta. Based on Southern blot analyses, the TCR alpha and beta gene loci appear to be arranged in translocon organ isation las opposed to multicluster) with multiple V gene segments, some (D ) and J gene segments and a single or few C gene segments. Northern blot an alyses show expression of the TCR alpha and beta chains in thymus, spleen a nd head kidney, expression of the TCR beta chain was also detected in the o vary. Interestingly, no expression was detected in intestine even though th e existence of T-cells in intestine has been proposed in other teleost spec ies. (C) 2000 Published by Elsevier Science Ltd.