Molecular characterization and expression analysis of T cell receptor (TCR) γ and δ genes in dojo loach (Misgurnus anguillicaudatus) in response to bacterial, parasitic and fungal challenge.

In mammalian, T-cell receptors (TCRs) play a key role in recognizing the presented antigen from external to protect organisms against environmental pathogens. To understand the potential roles of TCRγ and TCRδ in dojo loach (Misgurnus anguillicaudatus), Ma-TCRγ and Ma-TCRδ cDNAs were cloned and their gene expression profiles were investigated after bacterial, parasitic and fungal challenge. The open reading frame (ORF) of Ma-TCRγ and Ma-TCRδ cDNAs contained 948 and 867 bp, encoding 316 and 288 amino acid residues, respectively. Structurally, Ma-TCRγ and Ma-TCRδ were consisted of a signal peptide, a variable region, a constant region (IgC), a connecting peptide (CPS), a transmembrane region (TM) and a cytoplasmic domain (CYT), which were similar to those of other vertebrates. Multiple sequence alignment and phylogenetic analysis showed Ma-TCRγ and Ma-TCRδ were closely related to fish of Cyprinidae family. Ma-TCRγ and Ma-TCRδ were widely expressed in all tested organs/tissues, as the highest expressions of Ma-TCRγ and Ma-TCRδ were detected in kidney and gill, respectively. In addition, three infection models of dojo loach with bacteria (F. columnare G4), parasite (Ichthyophthirius multifiliis) and fungus (Saprolegnia sp.) were constructed. The morphological changes of gills and skin after challenged with F. columnare G4 and Ichthyophthirius multifiliis were investigated. Compared to F. columnare G4 infection, mRNA expression of both TCRγ and TCRδ showed higher sensitivity in classical immune organs (kidney and spleen) and mucosal tissues (skin and gill) after challenge with Ichthyophthirius multifiliis and Saprolegnia sp. Our results first indicated that TCRγ and TCRδ of dojo loach might function differently in response to challenge with different pathogens.