Identification and expression of a ferritin homolog in amphioxus Branchiostoma belcheri: evidence for its dual role in immune response and iron metabolism.

Ferritin plays a key role in cellular iron metabolism including iron storage and detoxification, which has been identified in a wide range of organisms including bacteria, fungi, plants and animals. However, little information is available regarding ferritin in the protochordates to date. Here we demonstrate the presence of a ferritin gene homolog, BbFRT, in amphioxus Branchiostoma belcheri. Analysis of the BbFRT 5'-UTR indicated the existence of a putative iron-responsive element (IRE) with a predicated stem-loop structure. BbFRT encoded a deduced protein of 172 amino acids with the conserved motif for ferroxidase center typical of heavy chains of vertebrate ferritins. Sequence comparison showed that BbFRT shared more identity to H-chains (68%) of vertebrate ferritins than to the L-chains (46-51%). Both in situ hybridization histochemistry and immunohistochemical staining revealed that BbFRT was ubiquitously expressed in B. belcheri. In addition, BbFRT expression was up-regulated by 1.6-fold and 1.5-fold, respectively, following exposure to LPS at both transcriptional and translational levels. Similarly, exposure to iron resulted in about 1.6-fold increase in BbFRT in the humoral fluids. These suggest that BbFRT seems a protein with a dual function functioning in both immune response and iron metabolism.