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

ABSTRACT: 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.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE55824 | GEO | 2014/06/08

SECONDARY ACCESSION(S): PRJNA241078

REPOSITORIES: GEO

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

Project description: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 RhinoM-bM-^@M-^Ys 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 5M-bM-^@M-^Yend 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. 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

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Cutoff suppresses RNA polymerase II termination to ensure expression of piRNA precursors

Project description:Small non-coding RNAs called piRNAs serve as the sequence-specific guides for an adaptable immune system that represses transposable elements in germ cells of Metazoa. The adaptation of the piRNA pathway to novel transposons is believed to occur when active transposons integrate into piRNA clusters, special genomic regions, which encode piRNA precursors. In Drosophila the RDC complex, composed of Rhino, Deadlock and Cutoff (Cuff) binds chromatin of dual-strand piRNA clusters and is required for transcription of piRNA precursors, though the mechanism by which RDC license transcription remained unknown. Here we show that Cuff prevents premature termination of RNA polymerase II by two distinct mechanisms. First, Cuff prevents cleavage of nascent RNA at poly(A) sites by interfering with recruitment of the cleavage and polyadenylation specificity factor (CPSF) complex. Second, if processing does occur, Cuff protects processed transcripts from degradation by the exonuclease Rat1. Our work reveals a conceptually novel mechanism of transcriptional enhancement. In contrast to other factors that regulate termination by binding to specific signals on nascent RNA, the RDC complex inhibits termination in a chromatin-dependent and sequence-independent manner.

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Project description:Piwi-Interacting RNAs (piRNAs) are central components of the piRNA pathway, which directs transposon silencing and guarantees genome integrity in the germ cells of several metazoans. In Drosophila, piRNAs are produced from discrete regions of the genome termed piRNA clusters, whose expression relies on the RDC complex comprised of the core proteins Rhino, Deadlock and Cutoff. To date, the RDC complex has been exclusively implicated in the regulation of the piRNA loci. Here we further elucidate the function of Cutoff and the RDC complex by performing genome-wide ChIP-seq and RNA-seq assays in the Drosophila germline and analyzing these data together with other publicly available data sets. In agreement with previous studies, we confirm that Cutoff is involved in the transcriptional regulation of piRNA clusters and in the repression of transposable elements in germ cells. Surprisingly, however, we find that Cutoff is enriched at and affects the expression of other non-coding RNAs, including spliceosomal RNAs (snRNAs) and small nucleolar RNAs (snoRNAs). At least in some instances, Cutoff appears to act at a transcriptional level in concert with Rhino and perhaps Deadlock. Finally, we show that mutations in Cutoff result in the deregulation of hundreds of protein-coding genes in germ cells. Our study uncovers a broader function for the RDC complex in the Drosophila germline development.

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Piwi is required during Drosophila embryogenesis to license dual-strand piRNA clusters for transposon repression in adult ovaries [RNA-seq]

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Splicing-independent loading of TREX on nascent RNA is required for efficient transcription of dual-strand piRNA clusters in Drosophila

Project description:The conserved THO/TREX complex is critical for pre-mRNA processing and mRNA nuclear export. In Metazoa, TREX is loaded on nascent RNA transcribed by RNA polymerase II in a splicing-dependent fashion; however, how TREX functions is poorly understood. Here we show that Thoc5 and other TREX components are essential for the biogenesis of piRNA, a distinct class of small non-coding RNAs that control expression of transposable elements (TE) in the Drosophila germline. Mutations in TREX lead to defects in piRNA biogenesis resulting in derepression of multiple TE families, gametogenesis defects, and sterility. TREX components are enriched on piRNA precursors transcribed from dual-strand piRNA clusters and co-localize in distinct nuclear foci that overlap with sites of piRNA transcription. The localization of TREX in nuclear foci and its loading on piRNA precursor transcripts depends on Cutoff, a protein associated with chromatin of piRNA clusters. Finally, we show that TREX is required for accumulation of nascent piRNA precursors. Our study reveals a novel splicing-independent mechanism for TREX loading on nascent RNA and its importance in piRNA biogenesis.

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Euchromatic transposon insertions trigger production of novel pi- and endo-siRNAs at the target sites in the Drosophila germline

Project description:The control of transposable element (TE) activity in germ cells provides genome integrity over generations. A distinct small RNA-mediated pathway utilizing Piwi-interacting RNAs (piRNAs) suppresses TE expression in gonads of metazoans. In the fly, primary piRNAs derive from so-called piRNA clusters, which are enriched in damaged repeated sequences. These piRNAs launch a cycle of TE and piRNA cluster transcript cleavages resulting in the amplification of piRNA and TE silencing. Using genome-wide comparison of TE insertions and ovarian small RNA libraries from two Drosophila strains, we found that individual TEs inserted into euchromatic loci form novel dual-stranded piRNA clusters. Formation of the piRNA-generating loci by active individual TEs provides a more potent silencing response to the TE expansion. Like all piRNA clusters, individual TEs are also capable of triggering the production of endogenous small interfering (endo-si) RNAs. Small RNA production by individual TEs spreads into the flanking genomic regions including coding cellular genes. We show that formation of TE-associated small RNA clusters can down-regulate expression of nearby genes in ovaries. Integration of TEs into the 3' untranslated region of actively transcribed genes induces piRNA production towards the 3'-end of transcripts, causing the appearance of genic piRNA clusters, a phenomenon that has been reported in different organisms. These data suggest a significant role of TE-associated small RNAs in the evolution of regulatory networks in the germline. The fractions of small RNAs (19-29 nt) from ovaries of y[1]; cn[1] bw[1] sp[1] line of Drosophila melanogaster were sequenced using Illumina HiSeq 2000.

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