CRISPR/cas9, a novel genomic tool to knock down microRNA in vitro and in vivo.

MicroRNAs are small and non-coding RNA molecules with the master role in regulation of gene expression at post-transcriptional/translational levels. Many methods have been developed for microRNA loss-of-function study, such as antisense inhibitors and sponges; however, the robustness, specificity, and stability of these traditional strategies are not highly satisfied. CRISPR/cas9 system is emerging as a novel genome editing tool in biology/medicine research, but its indication in microRNA research has not been studied exclusively. In this study, we clone CRISPR/cas9 constructs with single-guide RNAs specifically targeting biogenesis processing sites of selected microRNAs; and we find that CRISPR/cas9 can robustly and specifically reduce the expression of these microRNAs up to 96%. CRISPR/cas9 also shows an exclusive benefit in control of crossing off-target effect on microRNAs in the same family or with highly conserved sequences. More significantly, for the first time, we demonstrate the long term stability of microRNA knockdown phenotype by CRISPR/cas9 in both in vitro and in vivo models.