Spatially Controlled MicroRNA Imaging in Mitochondria via Enzymatic Activation of Hybridization Chain Reaction.

Live-cell imaging of RNA in specific subcellular compartments is essential for elucidating the rich repertoire of cellular functions, but it has been limited by a lack of simple, precisely controlled methods. Here such an approach is presented via the combination of hybridization chain reaction and spatially restricted enzymatic activation with organelle-targeted delivery. The system can localize engineered DNA hairpins in the mitochondria, where target RNA-initiated chain reaction of hybridization events is selectively activated by a specific enzyme, enabling amplified RNA imaging with high precision. It is demonstrated that the approach is compatible with live cell visualization and enables the regulatable imaging of microRNA in mitochondria. Since in situ activation of the signal amplification with enzyme eliminates the need for genetically encoded protein overexpression, it is envisioned that this simple platform will be broadly applicable for precise RNA imaging with subcellular resolution in a variety of biological processes.