Identification and characterization of a ferritin gene involved in the immune defense response of scallop Chlamys farreri

• A novel Chlamys farreri ferritin (CfFER) gene was identified and cloned.
• Sequence analysis was performed on the deduced amino acid sequence of CfFER.
• CfFER transcripts were ubiquitously expressed in all the examined tissues.
• Muscle and hemocyte displayed the highest and lowest expression levels of CfFER.
• CfFER mRNA expression sharply increased at 12 hpi and normalized at 48 hpi.

Scallop Chlamys farreri is an important aquaculture species in northern China. However, its mass mortality caused by several pathogens can result in great economic loss and negative impacts to the sustainable development of the scallop industry. Thus, improving the overall understanding of immune response mechanisms involved in host–pathogen interactions is necessary. Ferritins are conserved molecules in organisms that are involved in diverse biological processes, such as mediating host-pathogen responses. In this study, we report a novel ferritin gene from C. farreri (denoted as CfFER). The full length of CfFER is 848 bp and contains a 5′-UTR of 113 bp, a 3′-UTR of 219 bp, and a complete open reading frame (ORF) of 516 bp. The ORF encodes a polypeptide of 171 amino acid residues with a molecular weight of approximately 19.95 kDa and an isoelectric point of 5.07. The CfFER protein exhibited typical ferritin structures, namely, a ferroxidase diiron center, a ferrihydrite nucleation center, and an iron-binding response signature. Phylogenetic analysis revealed that CfFER was closely related to other mollusk ferritin proteins. Expression of CfFER in different tissues was analyzed by quantitative real-time PCR, and results showed that CfFER was ubiquitously expressed in all examined tissues. The highest and lowest expression levels of CfFER were measured in the muscle and hemocyte, respectively. The relative mRNA expression of CfFER in response to bacterial (Vibrio anguillarum) and viral (acute viral necrobiotic virus) challenges sharply increased by ca. 5-fold about12 h post-infection (hpi) and then normalized at 48 hpi. Western blot analysis with polyclonal antibodies generated from the recombinant product of CfFER also demonstrated the presence of ferritin protein in hemocytes. These findings strongly suggest that CfFER is involved in the immune response of C. farreri and protection against pathogen challenge.