Cloning and Expression Analysis of the Polymeric Immunoglobulin Receptor (pIgR) Gene in the Half Smooth Tongue Sole (Cynoglossus semilaevis)

Abstract:

In this study, the full-length cDNA sequence of the polymeric immunoglobulin receptor (pIgR) gene of the half-smooth tongue sole (Cynoglossus semilaevis) was obtained on the basis of its predicted sequence. The cDNA sequence was 1419 bp and included an open reading frame (1020 bp, encoding 339 amino acids), a 5¢-UTR region (109 bp), and a 3¢-UTR region (290 bp). Conserved domain analysis revealed that the pIgR protein of the half-smooth tongue sole contained one signal peptide, two immunoglobulin-like domains, and one transmembrane domain. According to the protein sequence homology alignment and phylogenetic tree analysis, the pIgR sequence of the half-smooth tongue sole had high similarity with the turbot (Scophthalmus maximus) and Japanese flounder (Paralichthys olivaceus) pIgR sequences. Real-time PCR analysis of pIgR expression in different tissues of healthy half-smooth tongue sole showed that the highest expression was in the gill and the lowest expression in muscles. After pathogen challenge with Vibrio harveyi, pIgR expression initially increased and then decreased in five tissues (liver, spleen, kidney, intestine, and gill) of the half-smooth tongue sole, with the peak time point being at 48 h in the spleen and gill, and 72 h in the liver, kidney, and intestine. Unlike in the internal organs, pIgR expression in the skin was continually upregulated. These results indicate that pIgR is involved in the immune response of the half-smooth tongue sole toward bacterial pathogens, and this finding may contribute to the discovery of an antibacterial gene marker.