Abstract
MicroRNAs are small noncoding RNAs regulating gene expression, through base paring with their target mRNAs, which have been actively investigated as key regulators in a wide range of biological processes. Conventional methods such as Northern blot are generally time-consuming, non-repeatable, and cannot be applied in vivo due to the requirement for cell fixation. Therefore, a noninvasive imaging system is required for the monitoring of microRNA biogenesis to understand the versatile functions of microRNAs in vivo as well as in vitro and to accelerate the clinical application of microRNA-based therapy. In this paper, we reviewed noninvasive molecular imaging systems for the monitoring of the biogenesis of microRNAs and post-transcriptional regulation of genes by microRNAs and the roles of microRNAs in various biological processes.