A genome-wide survey of NOD-like receptors in Chinese tongue sole (Cynoglossus semilaevis): Identification, characterization, and expression analysis in response to bacterial infection.

As intracellular pathogen recognition receptors (PRRs), nucleotide-binding domain, leucine-rich repeat containing receptors (NLRs, NOD-like receptors) are involved in innate immune responses in vertebrates. However, there is no systemic study on NLRs in Chinese tongue sole (Cynoglossus semilaevis), one of the popular maricultured fish in China. In the present study, a genome-wide survey of NLRs was performed in C. semilaevis, with the identification of 29 NLRs, including 5 genes from NLR-A subfamily (referred to as CsNOD1-5), two genes from NLR-B subfamily, 18 genes from NLR-C subfamily (referred to as CsNLR-C1 to 18), and four other NLR genes. Phylogenetic analysis implied that CsNOD1-5 contained conserved functional domains and had orthologous relationships with human NOD1-5. Moreover, CsNLR-C genes all possessed FISHNA domain, which is a fish-specific NACHT subdomain. Expression analysis showed that CsNOD1-5 and CsNLR-C1/2 were ubiquitously expressed in various normal tissues. Bacterial infection with Vibro harveyi revealed that distinct expression patterns of all the tested CsNLRs in gill, intestine, trunk kidney, liver and spleen. Especially, CsNOD1-4 and CsNLR-C2 were significantly up-regulated in gill at 48 h post bacterial infection. Besides, CsNOD3 and CsNOD4which were significantly elevated in infectious intestine, trunk kidney, liver and spleen, revealed that their expressions were more sensitive to bacterial infection than other CsNLRs. Together with the computational protein-protein interaction network of CsNLRs, it was suggested the different roles of individual NLR gene in the innate immune cascades of C. semilaevi against bacterial infection. This study would provide valuable information for the further studies on CsNLRs' immune function. This article is protected by copyright. All rights reserved.