MicroRNAs (miRNAs) are single-stranded non-coding RNAs of ~22 nucleotides, which can negatively regulate
gene expression through induction of mRNA degradation and/or post-transcriptional gene silencing. MiRNAs are key
factors in the regulation of many biological processes such as cell proliferation, differentiation, and death. Since miRNAs
are known to be in close association with cancer development, non-invasive imaging of miRNA expression and/or activity
is of critical importance, for which conventional molecular biology techniques are not suitable or applicable. Over the last
several years, various molecular imaging techniques have been investigated for imaging of miRNAs. In this review article,
we summarize the current state-of-the-art imaging of miRNAs, which are typically based on fluorescent proteins, bioluminescent
enzymes, molecular beacons, and/or various nanoparticles. Non-invasive imaging of miRNA expression
and/or biological activity is still at its infancy. Future research on more clinically relevant, non-toxic techniques is required
to move the field of miRNA imaging into clinical applications. Non-invasive imaging of miRNA is an invaluable
method that can not only significantly advance our understandings of a wide range of human diseases, but also lead to
new and more effective treatment strategies for these diseases.
Keywords: microRNA (miRNA), bioluminescence imaging (BLI), fluorescence imaging, magnetic resonance imaging (MRI),
molecular imaging, cancer, nanomedicine.
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