Uridylation of hairpin-RNAs by Tailor confines the emergence of miRNAs in Drosophila

Uridylation of diverse RNA species represents an emerging theme in post-transcriptional gene regulation. In the microRNA pathway, such modifications regulate small RNA biogenesis and stability in plants, worms and mammals. Here, we report the first uridylyltransferase that acts on small RNAs in Drosophila, which we refer to as Tailor. Tailor is the source for the majority of 3´ end-modifications in microRNAs and predominantly targets precursor-hairpins. Uridylation modulates the characteristic two-nucleotide 3´ overhangs of microRNA hairpins, which regulates processing by Dicer-1 and destabilizes RNA hairpins. Furthermore, Tailor preferentially uridylates mirtron-hairpins, thereby impeding the production of non-canonical microRNAs. Mirtron-selectivity is explained by unique primary sequence specificity of Tailor, selecting RNA substrates ending with a 3´ guanosine, a feature not previously observed for TUTases. In contrast to mirtrons, conserved Drosophila pre-miRNAs are significantly depleted in 3´ guanosine, thereby escaping regulatory uridylation. Our data support the hypothesis that evolutionary adaptation to pre-miRNA uridylation shapes the nucleotide composition of pre-miRNA 3´ ends. Hence, hairpin-uridylation may serve as a barrier for the de novo creation of miRNAs in Drosophila. Overall design: mRNA sequencing of Drosophila S2 cells (3-times; control libraries) and three biological replicates of S2 cells stably depleted of CG1091/Tailor by CRISPR/Cas9

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Reimão-Pinto MM, Ignatova V, Burkard TR, Hung JH, Manzenreither RA, Sowemimo I, Herzog VA, Reichholf B, Fariña-Lopez S, Ameres SL