Understanding functional miRNA–target interactions in vivo by site-specific genome engineering

MicroRNA (miRNA) target recognition is largely dictated by short ‘seed’ sequences, and single miRNAs therefore have the potential to regulate a large number of genes. Understanding the contribution of specific miRNA–target interactions to the regulation of biological processes in vivo remains challenging. Here we use transcription activator-like effector nuclease (TALEN) and clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 technologies to interrogate the functional relevance of predicted miRNA response elements (MREs) to post-transcriptional silencing in zebrafish and Drosophila. We also demonstrate an effective strategy that uses CRISPR-mediated homology-directed repair with short oligonucleotide donors for the assessment of MRE activity in human cells. These methods facilitate analysis of the direct phenotypic consequences resulting from blocking specific miRNA–MRE interactions at any point during development.