Ferritin-based reporter genes for magnetic resonance imaging in the brain

Understanding the central role of neurotransmitters in human cognition has motivated a need for non-invasive imaging of the brain on a molecular and cellular level. Unlike other organs, the brain is difficult to access without damaging the whole organism and destroying the behavioral context. In addition, molecular-genetic changes precede disease symptoms and information about protein transcription can improve early diagnosis. The development of gene and cell therapy in the central nervous system depends on reliable non-invasive monitoring of local gene expression. Use of reporter genes such as green fluorescent protein has revolutionized molecular biology, however the attenuation of light in tissue limits the penetration depth and confines in vivo experiments to superficial regions.;The goal of the present research is to improve ferritin-based reporter systems. We use a semi-quantitative method for measuring ferritin expression in the mouse brain by correlation of the transverse relaxation rate with the number of inoculated viral particles. We design and characterize a novel ferritin-based chimera with enhanced MRI sensitivity. We use this improved reporter in vivo to track the migration of neural progenitors towards the murine olfactory bulb. Finally, we quantify the changes of several iron import proteins in cells expressing the MRI reporter. We use the data to model the molecular pathway that ferritin-based reporters utilize to load iron in situ.;Magnetic resonance imaging (MRI) is inherently three-dimensional with high resolution and no depth penetration limit. Also, it does not use ionizing radiation so it is safe and well suited for longitudinal studies. The iron storage protein ferritin has been successfully used as an MRI reporter gene in both vector mediated gene delivery and transgenic animal models. Upon transgene expression ferritin forms a paramagnetic ferrihydrite core that imparts MRI contrast. Imaging ferritin still suffers relatively low sensitivity and lack of methods for quantitation. Importantly, little is known about the iron loading pathways that ferritin utilizes when expressed as a reporter in the brain.