Molecular Characterization and Expression Analyses of the Complement Component C8α, C8β and C9 Genes in Yellow Catfish (Pelteobagrus fulvidraco) after the Aeromonas hydrophila Challenge

The complement components C8 alpha, C8 beta and C9 have important roles in the innate immune system against invading microorganisms. Partial cDNA sequences of the Pf_C8 alpha, Pf_C8 beta and Pf_C9 genes (Pf: abbreviation of Pelteobagrus fulvidraco) were cloned from yellow catfish. The Pf_C8 alpha, Pf_C8 beta and Pf_C9 genes showed the greatest amino acid similarity to C8 alpha (54%) and C8 beta (62%) of zebrafish and to C9 (52%) of grass carp, respectively. Ontogenetic expression analyses using real-time quantitative PCR suggested that the three genes may play crucial roles during embryonic and early larval development. The mRNA expressions of the three genes were all at the highest levels in liver tissue, and at lower or much lower levels in 16 other tissues, demonstrating that the liver is the primary site for the protein synthesis of Pf_C8 alpha, Pf_C8 beta and Pf_C9. Injection of Aeromonas hydrophila led to up-regulation of the three genes in the spleen, head kidney, kidney, liver and blood tissues, indicating that the three genes may contribute to the host's defense against invading pathogenic microbes. An increased understanding of the functions of the Pf_C8 alpha, Pf_C8 beta and Pf_C9 genes in the innate immunity of yellow catfish will help enhance production of this valuable freshwater species.