L-rhamnose-binding lectins (RBLs) in Nile tilapia, Oreochromis niloticus: characterization and expression profiling in mucosal tissues

Authors: ZHANG, DONGDONG - Auburn University; Beck, Benjamin; MOHAMMED, HAITHAM - Auburn University; ZHAO, HONGGANG - Auburn University; THONGDA, WILAWAN - Auburn University; YE, ZHI - Auburn University; ZENG, QIFAN - Auburn University; Shoemaker, Craig; Fuller, Adam; PEATMAN, ERIC - Auburn University

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2017
Publication Date: 1/5/2018
Citation: Zhang, D., Beck, B.H., Mohammed, H., Zhao, H., Thongda, W., Ye, Z., Zeng, Q., Shoemaker, C.A., Fuller, S.A., Peatman, E. 2018. L-rhamnose-binding lectins (RBLs) in Nile tilapia, Oreochromis niloticus: characterization and expression profiling in mucosal tissues. Fish and Shellfish Immunology. 72:426-435.

Interpretive Summary: Rhamnose-binding lectins (RBLs) are important molecules in the immune response to infections and have been characterized from a variety of fish species. Our previous work highlighted a major role of a RBL (IpRBL1a) in controlling the early adhesion of a bacterial pathogen called Flavobacterium columnare. We found that IpRBL1a was more abundant in the gill of susceptible channel catfish (Ictalurus punctatus) under normal conditions and following infection. Given the importance of RBL in channel catfish, we sought to study the diversity of RBLs in another important cultured fish, Nile tilapia (Oreochromis niloticus) and their abundance after experimental infection with Streptococcus agalactiae, one of the diseases in farmed tilapia. In this study, four RBL genes were identified from Nile tilapia and were designated as OnRBL3a, OnRBL3b, OnRBL3c, and OnRBL3d. OnRBLs had the highest expression in immune-related tissues including the gill, intestine and liver. However, the changes of OnRBL expression in the gill and intestine at 2 h, 4 h and 24 h post S. agalactiae challenge were modest, suggesting that tilapia may not moderate S. agalactiae infections through their RBL genes. This expression pattern may be correlated with the type of RBL present in tilapia, the disease process of S. agalactiae, and the species of fish host. The RBLs characterized in this study were the first RBL members identified in Nile tilapia and their characterization will expand our knowledge of the role played by RBLs in mucosal immunity.

Technical Abstract: Rhamnose-binding lectins (RBLs) are crucial elements associated with innate immune responses to infections and have been characterized from a variety of teleost fishes. Our previous work highlighted a major role of a RBL (IpRBL1a) in mediating F. columnare adhesion and IpRBL1a showed higher expression in the gill of susceptible channel catfish (Ictalurus punctatus) under basal conditions and following infection. Given the importance of RBL in teleost fishes and its new characterization in channel catfish, we sought to study the diversity of RBLs in another important cultured fish, Nile tilapia (Oreochromis niloticus) and their mucosal expression profiles following experimental infection with Streptococcus agalactiae, one of the major causes of streptococcosis in farmed tilapia. In this study, four RBL genes were identified from Nile tilapia and were designated as OnRBL3a, OnRBL3b, OnRBL3c, and OnRBL3d. These OnRBLs were composed of two tandem-repeated type five carbohydrate recognition domains (CRDs), classified as type IIIc, and all clustered together in the phylogenetic tree. OnRBL-CRDs shared conserved topology of eight half-cysteine residues, characteristic peptide motifs of -YGR- and -DPC- (or -FGR- and -DTC-), and similar exon/intron organization. OnRBLs had the highest expression in immune-related tissues, gill, intestine or liver. However, the changes of OnRBL expression in the gill and intestine at 2 h, 4 h and 24 h post S. agalactiae challenge were modest, suggesting that tilapia may not mediate the entry or confront the infection of S. agalactiae through highly inducing the expression of these RBL genes. This expression pattern may be correlated with the type of RBL and CRD composition, the pathogenesis of S. agalactiae, and the species of fish host. OnRBLs characterized in this study were the first RBL members identified in Nile tilapia and their characterization will expand our knowledge of the role played by RBLs in mucosal immunity.