The Rhino-Deadlock-Cutoff complex licenses non-canonical transcription of dual-strand piRNA clusters in Drosophila. Drosophila melanogaster

Argonaute proteins of the PIWI clade are central to transposon silencing in animal gonads. Their target specificity is defined by 22-30nt PIWI interacting RNAs (piRNAs), which mostly originate from discrete genomic loci termed piRNA clusters. Here we show that the RDC complex composed of Rhino, Deadlock and Cutoff defines dual-strand piRNA clusters genome-wide in Drosophila ovaries. The RDC complex is anchored to H3K9me3-marked chromatin in part via Rhino’s chromo-domain. Depletion of Piwi results in loss of the RDC and small RNAs at euchromatic piRNA source loci, demonstrating a feedback loop between Piwi and genomic piRNA sources. Intriguingly, profiles of RNA Polymerase II occupancy, nascent transcription and steady-state RNA levels reveal that the RDC licenses non-canonical transcription of dual-stranded piRNA clusters. Likely, this process involves 5’end protection of nascent RNAs and subsequent suppression of transcription termination. Together, our data provide a comprehensive model for the regulation and evolution of piRNA clusters. Overall design: This study aims at indentifying and characterizing genimc sources of piRNA percursour transcripts using genome-wide apporaches such as ChIP-seq, RNA-seq, smallRNA-seq and GRO-seq in adult Drosophila ovaries depleted for several factors implicated in piRNA cluster regulation