Characterization of Complement Regulatory Genes in Channel Catfish and Their Involvement in Disease Defense Response

Channel catfish (Ictalurus punctatus) is the leading aquaculture species in the United States in spite of a downward trend in production due to disease losses in recent years. Innate immunity plays a crucial role in disease defense responses in channel catfish. Complement system is one of the most important defense system in innate immunity. Numerous studies have been conducted to characterize immune-related genes in channel catfish such as pathogen recognition receptors, while analyses of complement regulatory genes have been limited. In this study, we identified 12 complement regulatory genes from the channel catfish genome. Phylogenetic analysis and syntenic analysis were conducted to determine their orthology relationships, supporting their correct annotation. The expression profiles of the complement regulatory genes were determined after infection with two main bacterial disease pathogens, Edwardsiella ictaluri and Flavobacterium columnare. The results indicated that seven genes were significantly up-regulated in the skin of catfish after infection with E. ictaluri, while five were significantly down-regulated after infection with F. columnare, suggesting their critical roles in the host immune response to bacterial pathogens. This is the first systematic analysis of complement regulatory genes and their involvement in disease defense responses in channel catfish.