Identification and characterization of a Macrobrachium nipponense ferritin subunit regulated by iron ion and pathogen challenge.

Ferritin, a major iron storage protein in most living organisms, plays a crucial role in iron metabolism. In this study, the ferritin subunit MnFer was identified in the oriental river prawn (Macrobrachium nipponense) and functionally characterized. The full-length cDNA of MnFer is 999 bp in size with a 122-bp 5'-untranslated region (UTR), a 364-bp 3'-UTR and a 513-bp open reading frame that encodes a protein possessing 171 amino acids and a deduced molecular weight of 19.40 kDa. Prawn ferritin transcripts are expressed in muscle, heart, hepatopancreas, gill, hemocytes, ovary and testis. Quantitative real-time PCR revealed that the abundance of ferritin transcript was highest in the hepatopancreas followed by muscle. Ferritin transcript expression in muscle increased six-fold 3 h after the injection of iron. In the gill, a four-fold increase in ferritin transcript expression was detected 3 h post-injection; the expression remained elevated for 48 h. Heart ferritin mRNA expression increased up to seven-fold at 24 h post-injection. No significant difference was found in the hepatopancreas. The iron binding capacity of recombinant ferritin protein was also demonstrated in this study. In hemocyte experiments, the transcriptional expression of MnFer showed the strongest response to Aeromonas hydrophila. As a whole, our study suggested that the ferritin from M. nipponense may play critical roles in cellular and organismic iron homeostasis along with in innate immune defense.