Complementary DNA sequences of the constant regions of T ‐cell antigen receptors α, β and γ in mandarin fish, S iniperca chuatsi Basilewsky, and their transcriptional changes after stimulation with F lavobacterium columnare

In this study, the constant‐region genes ( C α, C β and C γ) that encode the T ‐cell antigen receptor ( TCR ) α, β and γ chains were cloned from mandarin fish, S iniperca chuatsi Basilewsky, an important freshwater fish species in C hina. The complementary DNA sequences of C α, C β and C γ were 843, 716 and 906 base pairs (bp) in length and had a 465‐, 289‐ and 360‐bp 3′ untranslated region, encoding 125, 142 and 182 amino acids, respectively. The amino‐acid sequences of the constant regions of mandarin fish TCR α, β and γ chains (encoded by C α, C β and C γ, respectively) were most similar to those of their teleost counterparts, showing 60% similarity with pufferfish, 48% similarity with A tlantic salmon and 57% similarity with flounder, respectively. The phylogenetic analysis revealed that the mandarin fish C α, C β and C γ were clustered, respectively, with their vertebrate counterparts. The mandarin fish C α, C β and C γ could also be separated into four domains: immunoglobulin; connecting peptide ( CP ); transmembrane ( TM ); and cytoplasmic tail. Several conserved features in mammalian TCR s were also found in those of mandarin fish, such as a conserved cysteine residue in the CP domain of C α, necessary for creating an interchain disulphide bond with the TCR β chain, and a conserved antigen receptor TM motif in C α and C β. Meanwhile, transcripts of C α, C β and C γ were detectable in all examined organs, with a stronger signal observed in lymphoid organs. In addition, the temporal transcriptional changes for C α and C γ were investigated, 1, 2, 3, 4, 5, 6 and 8 weeks after stimulation with F lavobacterium columnare , in head kidney, spleen, blood, thymus, gill and intestine, using real‐time polymerase chain reaction. The results demonstrated stimulation‐dependent up‐regulations in almost all tissues examined, which indicates that T cells may play important roles in preventing mandarin fish from bacterial invasion. In particular, apart from thymus, T cells were distributed mainly in gill and intestine, where striking up‐regulation of C γ was also observed. These results will facilitate functional studies of teleost TCR s and T cells.