MRI detection of transcriptional regulation of gene expression in transgenic mice

Abstract

Ferritin, the iron storage protein, was recently suggested to be a candidate reporter for the detection of gene expression by magnetic resonance imaging (MRI). Here we report the generation of TET:EGFP-HAferritin (tet-hfer) transgenic mice, in which tissue-specific inducible transcriptional regulation of expression of the heavy chain of ferritin could be detected in vivo by MRI. We show organ specificity by mating the tet-hfer mice with transgenic mice expressing tetracycline transactivator (tTA) in liver hepatocytes and in vascular endothelial cells. Tetracycline-regulated overexpression of ferritin resulted in specific alterations of the transverse relaxation rate (R(2)) of water. Transgene-dependent changes in R(2) were detectable by MRI in adult mice, and we also found fetal developmental induction of transgene expression in utero. Thus, the tet-hfer MRI reporter mice provide a new transgenic mouse platform for in vivo molecular imaging of reporter gene expression by MRI during both embryonic and adult life.

Evaluation of the specificity and sensitivity of ferritin as an MRI reporter gene in the mouse brain using lentiviral and adeno-associated viral vectors

“…16 Transgenic mice expressing FerrH in a tissue-specific and tetracycline-dependent manner, show tissuedependent changes in T 2 values that could be detected by MRI. 17 The feasibility of using an iron-sequestering protein as an MRI reporter by in situ viral vector-mediated delivery was demonstrated by Genove et al 10 An adenoviral vector was used to transiently overexpress human FerrH in the mouse brain, which resulted in significant hypointense (that is, dark) MRI contrast at the site of vector injection. 10 However, the sensitivity of the reported systems is limited.…”

(Strept)avidin-displaying lentiviruses as versatile tools for targeting and dual imaging of gene delivery

“…Ferritin was chosen as a transgene to study the success of lentiviral gene delivery to the rat brain, as it requires no exogenous contrast agents for detection by MRI. [22][23][24] Hemorrhage caused by injection appeared on T2*-weighted gradientecho images of all animals at day 3 but as acute hematoma resolved within a few days, 43 only the specific signal from ferritin was detected. The MRI contrast was seen during the entire 7-month time course investigated, thus confirming stable expression of ferritin in the brain.…”

“…[22][23][24] To evaluate the ability of human heavy chain of ferritin (hHF) expressing lentivirus to increase iron uptake in vitro, we measured relaxation rate R2 (R2 ¼ 1/T2) in AVD/GP64-hHF-transduced HepG2 cells 48 h post-transduction (p.t.) ( Figure 3).…”

Using magnetic resonance imaging and spectroscopy in cancer diagnostics and monitoring

“…The targeted contrast agents have greatly increased molecular specificity of biological targets to be imaged by MRI, such as receptors 146 and products of transgenes. 147,148 Most of the contrast agents offer good specificity to the given target by enhancing either T 1 and/ or T 2 relaxation. The former agents provide positive contrast in T 1 -images, and the latter ones negative contrast in T 2 -images.…”