Molecular characterization and gene expression of the channel catfish ferritin H subunit after bacterial infection and iron treatment.

Ferritins are the major iron storage protein in the cytoplasm of cells, responsible for regulating levels of intracellular iron. Ferritin genes are widely distributed in both prokaryotes and eukaryotes. In mammals, ferritin molecules are composed of heavy- (H) and light- (L) chain subunits; amphibian genomes contain three ferritin-type genes (H; middle, M; and L subunits); and teleost genomes to date contain H and M subunits. The objective of this study was to characterize the ferritin H gene in channel catfish (Ictalurus punctatus) to determine its genomic organization and copy numbers, to determine its patterns of tissue expression, and to establish if it is involved in defense responses of catfish after bacterial infection. The catfish ferritin H gene was completely sequenced and characterized, using both mRNA and genomic DNA. Catfish ferritin H gene has a full-length mRNA sequence of 999 bp, an open reading frame of 534 bp, and 4,704 bp genomic DNA sequence. Catfish ferritin H has a 5 exon and 4 intron genetic organization, containing a long 5'-untranslated region, which shares high similarity with mammalian and zebrafish genes. Based on phylogenetic analyses, the catfish ferritin H gene is highly conserved throughout evolution. Southern blot analysis suggested that the ferritin H gene has only one copy in the catfish genome. The catfish ferritin H gene was widely expressed in various healthy tissues. The catfish ferritin H gene was significantly up-regulated in the liver after intraperitoneal injection of iron dextran and coinjection of Edwardsiella ictaluri and iron dextran treatment, suggesting its role in iron metabolism and immunity.