PIWI Slicing and RNA Elements in Precursors Instruct Directional Primary piRNA Biogenesis
David Homolka6, Radha Raman Pandey6, Coline Goriaux, Emilie Brasset, Chantal Vaury, Ravi Sachidanandam, Marie-Odile Fauvarque, Ramesh S. Pillaicorrespondenceemail
6Co-first author
Publication stage: In Press Corrected Proof
Highlights
•A piRNA-trigger sequence from the 5′ end of a fly cluster drives primary processing
•Slicer activity of PIWI generates non-overlapping, contiguous primary piRNAs
•Cytoplasmic PIWI-triggered primary piRNAs are loaded into nuclear PIWI
•Primary piRNA biogenesis proceeds with a 5′–3′ directionality
Summary
PIWI proteins and PIWI-interacting RNAs (piRNAs) mediate repression of transposons in the animal gonads. Primary processing converts long single-stranded RNAs into ∼30-nt piRNAs, but their entry into the biogenesis pathway is unknown. Here, we demonstrate that an RNA element at the 5′ end of a piRNA cluster—which we termed piRNA trigger sequence (PTS)—can induce primary processing of any downstream sequence. We propose that such signals are triggers for the generation of the original pool of piRNAs. We also demonstrate that endonucleolytic cleavage of a transcript by a cytosolic PIWI results in its entry into primary processing, which triggers the generation of non-overlapping, contiguous primary piRNAs in the 3′ direction from the target transcript. These piRNAs are loaded into a nuclear PIWI, thereby linking cytoplasmic post-transcriptional silencing to nuclear transcriptional repression.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Received: March 12, 2015; Received in revised form: May 12, 2015; Accepted: June 5, 2015; Published Online: July 09, 2015
© 2015 The Authors. Published by Elsevier Inc.
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