Detection of intracellular microRNA using a self-assembling magnetic resonance beacon

MicroRNAs (miRNAs or miRs) are implicated in several biological processes such as proliferation, differentiation, apoptosis, development and disease. A number of miRNA imaging tools have been developed due to the scientific and clinical significance of miRNA. Current miRNA imaging techniques are based on reporter gene and molecular beacon systems, and most of these techniques utilize fluorescent probes. These techniques have been successfully used to study the function and interaction of miRNAs in the cellular environment. However, they have limited clinical applicability as imaging systems, mainly due to the inability of fluorescent probes to penetrate tissue. Magnetic resonance imaging (MRI) provides high resolution in three dimensions to analyze the anatomy and structure of tissues. We developed a self-assembling magnetic nanoparticle based molecular beacon (miR124a MR beacon) to detect miR124a in mammalian cells and tissues during neuronal differentiation by T2-weighted magnetic resonance (MR). The self-assembled structure of the miR124a MR beacons was induced by incubating 3’-adaptor, 5’-adaptor and miR linker containing the miR124a binding sequence and adaptor binding sequence. When the miR124a expression level was low in cells and tissues, the MR signal of the miR124a MR beacons was quenched. As the concentration of miR124a increased during neuronal differentiation, selective hybridization occurred between miR124a and the miR124a binding sequence of the miR124a MR beacon. This ultimately induced nanoparticle disassembly and a gradual increase in the MR signal. Our findings suggest that this method can be used to monitor the expression of miRNAs, as well as other intracellular genetic and cellular processes, by MR imaging in vivo .