The RNA-binding Protein TDP-43 Selectively Disrupts MicroRNA-1/206 Incorporation into the RNA-induced

MicroRNA (miRNA) maturation is regulated by interaction of particular miRNA precursors with specific RNA-binding pro- teins. Following their biogenesis, mature miRNAs are incorpo- rated into the RNA-induced silencing complex (RISC) where they interact with mRNAs to negatively regulate protein pro- duction. However, little is known about how mature miRNAs are regulated at the level of their activity. To address this, we screened for proteins differentially bound to the mature form of the miR-1 or miR-133 miRNA families. These muscle-enriched, co-transcribed miRNA pairs cooperate to suppress smooth muscle gene expression in the heart. However, they also have opposing roles, with the miR-1 family, composed of miR-1 and miR-206, promoting myogenic differentiation, whereas miR- 133 maintains the progenitor state. Here, we describe a physical interaction between TDP-43, an RNA-binding protein that forms aggregates in the neuromuscular disease, amyotrophic lateral sclerosis, and the miR-1, but not miR-133, family. Defi- ciency of the TDP-43 Drosophila ortholog enhanced dmiR-1 activity in vivo. In mammalian cells, TDP-43 limited the activity of both miR-1 and miR-206, but not the miR-133 family, by dis- rupting their RISC association. Consistent with TDP-43 damp- ening miR-1/206 activity, protein levels of the miR-1/206 tar- gets, IGF-1 and HDAC4, were elevated in TDP-43 transgenic mouse muscle. This occurred without corresponding Igf-1 or Hdac4 mRNA increases and despite higher miR-1 and miR-206 expression. Our findings reveal that TDP-43 negatively regu- lates the activity of the miR-1 family of miRNAs by limiting their bioavailability for RISC loading and suggest a processing-inde- pendent mechanism for differential regulation of miRNA activity.