Dual Functional Roles of Molecular Beacon: a MicroRNA Detector and Inhibitor

MicroRNAs are essential in many cellular processes. The ability to detect microRNAs is important for understanding its function and biogenesis. This study is aimed at using a molecular beacon to detect miR-430 in developing zebrafish embryos as a proof of principle. miR-430 is crucial for the clearance of maternal mRNA during maternal zygotic transition (MZT) in embryonic development. Despite its known function, the temporal and spatial expression of miR-430 remains unclear. We used various imaging techniques, including laser scanning confocal microscopy, spinning disk and lightsheet microscopy, to study the localization of miR-430 and any developmental defects possibly caused by the molecular beacon. Our results show that miR-430 is expressed early in development and is localized in distinct cytoplasmic granules where its target mRNA can be detected. We also show that the designed molecular beacon can inhibit the function of miR-430 and cause developmental defect in the brain, notochord, heart, and kidney, depending on the delivery site within the embryo suggesting that miR-430 plays a diverse role in embryonic morphogenesis. When compared with morpholino, molecular beacon is two orders of magnitude more potent in inhibiting miR-430. Thus, our results reveal that in addition to being used as a valuable tool for the detection of microRNAs in-vivo, molecular beacons can also be employed to inhibit microRNAs in a specific manner.