In this report, we generated a ferritin and red fluorescent protein fusion reporter gene that enables the visualization of transgene expression in living animals by magnetic resonance imaging (MRI) and optical imaging. Ferritin heavy chain (FTH) or light chain (FTL) was linked to the N terminus of the monomeric DsRed red fluorescent protein to create FTH-DsRed and FTL-DsRed, MRI-fluorescence dual reporters. Transfection of these dual reporters into cells resulted in increased iron loading and strong red fluorescence in cells. Adenoviral vectors to express FTH-DsRed or FTL-DsRed fusion reporter in infected cells were created, but only the adenovirus expressing FTH-DsRed resulted in a high level of red fluorescence in cells. Delivery and expression of FTH-DsRed in the mouse brain using adenovirus was detected by MRI and fluorescence imaging, revealing a T-2 shortening effect and an increase of contrast in T-2-weighted images at the sites co-localized with strong red fluorescence. While the details of the structure of ferritin-DsRed fusion reporter remains to be solved, this dual reporter is useful for visualizing dynamic processes such as the migration of reporter-transfected stem cells or metastasis of tumors using MRI with the added flexibility of combining optical tools such as fluorescence activated cell sorting and fluorescence microscopy.
