Rbfox3 Controls the Biogenesis of a Subset of MicroRNAs

RNA-binding proteins (RBPs) regulate numerous aspects of gene expression, thus identification of endogenous targets of RBPs is important for understanding their functions in cells. Here we identified transcriptome-wide targets of Rbfox3 in neuronally differentiated P19 cells and mouse brain using Photoactivatable-Ribonucleoside-Enhanced Crosslinking and Immunoprecipitation (PAR-CLIP). Although Rbfox3 is known to regulate pre-mRNA splicing through binding to the UGCAUG motif, PAR-CLIP analysis revealed diverse Rbfox3 targets including primary-microRNAs (pri-miRNAs) which lack the UGCAUG motif. Induced expression and depletion of Rbfox3 led to changes in the expression levels of a subset of PAR-CLIP-detected miRNAs. In vitro analyses revealed that Rbfox3 functions as a positive and a negative regulator at the stage of pri-miRNA processing to precursor-miRNA. Rbfox3 binds directly to pri-miRNAs and regulates the recruitment of the microprocessor complex to pri-miRNAs. Our study proposes a novel function for Rbfox3 in miRNA biogenesis.