Submitted to: Developmental and Comparative Immunology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/18/2014
Publication Date: 2/12/2014
Citation: Thongda, W., Li, C., Luo, Y.P., Beck, B.H., Peatman, E. 2014. L-rhamnose-binding lectins (RBLs) in channel catfish, Ictalurus punctatus: Characterization and expression profiling in mucosal tissues. Developmental and Comparative Immunology. 44(2):320-331. Interpretive Summary: Rhamnose binding-lectins (RBLs) are a family of molecules that have important functions in the immune system of fish. Previously, we found that fish that were highly susceptible to infection with Flavobacterium columnare, the causative agent of columnaris disease, had higher RBL levels in tissues such as the gill. In this study, we wanted to better understand the function of RBLs and to identify how many unique RBLs were present in channel catfish. We identified six different types of RBLs and examined how their levels responded to infection with columnaris disease and enteric septicemia of catfish, two bacterial diseases of commercial importance. The levels of each RBL varied widely between the two bacterial diseases. Also, the pattern of RBL expression was different between the various tissues examined. These findings suggest that each RBL may play a unique role in the host immune response to bacteria. Our findings improve our understanding of the immune system of cultured fish, and will help in identifying new preventatives and treatments for costly diseases.
Technical Abstract: Rhamnose binding-lectins (RBLs) have recently emerged as important molecules in the context of innate immunity in teleost fishes. Previously, using RNA-seq technology, we observed marked up-regulation of a RBL in channel catfish (Ictalurus punctatus) gill following a challenge with the bacterial pathogen Flavobacterium columnare. Furthermore, the magnitude of RBL up-regulation positively correlated with disease susceptibility. Moving forward from these findings, we wished to more broadly understand RBL function, diversity, and expression kinetics in channel catfish. Therefore, in the present study we characterized the RBL gene family present in select channel catfish tissues and profiled family member expression after challenge with two different Gram-negative bacterial pathogens. Here, six RBLs were identified from channel catfish and were designated IpRBL1a, IpRBL1b, IpRBL1c, IpRBL3a, IpRBL3b, and IpRBL5a. These RBLs contained carbohydrate recognition domains (CRD) ranging from one to three domains and each CRD contained the conserved motifs of –YGR- and –DPC-. Despite a level of structural conservation, the catfish RBLs showed low full-length identity with RBLs from outside the order Siluriformes. IpRBL expression after bacterial infection varied depending on both pathogen and tissue type, suggesting that IpRBLs may exert disparate functions or exhibit distinct tissue-selective roles in the host immune response to bacterial pathogens.