Preferential microRNA targeting revealed by in vivo competitive binding and differential Argonaute immunoprecipitation

MicroRNAs (miRNAs) have been described to simultaneously inhibit hundreds of targets, albeit to a modest extent. It was recently proposed that there could exist more specific, exceptionally strong binding to a subgroup of targets. However, it is unknown, whether this is the case and how such targets can be identified. Using RNA-seq with Argonaute2-ribonucleoprotein immunoprecipitation and in vivo competitive binding assays, researchers from the Technical University of Munich demonstrate for miRNAs-21, -199-3p and let-7 exceptional regulation of a subset of targets, which are characterized by preferential miRNA binding. They confirm this finding by analysis of independent quantitative proteome and transcriptome datasets obtained after miRNA silencing. Their results suggest that mammalian miRNA activity is guided by preferential binding of a small set of 3′-untranslated regions, thereby shaping a steep gradient of regulation between potential targets. They propose that this approach can be applied for transcriptome-wide identification of such targets independently of the presence of seed complementary sequences or other predictors.