Unknown,Transcriptomics,Genomics,Proteomics

Dataset Information

Transcriptional silencing of transposable elements by Piwi and its impact on chromatin and gene expression

ABSTRACT: Eukaryotic genomes are colonized by transposable elements whose uncontrolled activity results in genomic instability. The piRNA pathway silences transposons in animal gonads, yet how this is achieved molecularly remains controversial. We assign an essential role to the HMG protein Maelstrom in the process of Piwi mediated silencing in Drosophila. Genome wide assays revealed highly correlated changes in RNA Polymerase II recruitment, nascent RNA output and steady state RNA levels of transposons upon loss of Piwi or Maelstrom. Our data demonstrate piRNA-mediated trans- silencing of hundreds of transposon copies at the transcriptional level. We show that Piwi is required for establishing heterochromatic H3K9me3 marks on transposons and their genomic surrounding. In contrast, loss of Maelstrom impacts transposon H3K9me3 patterns only marginally yet leads to increased heterochromatin spreading, suggesting that Maelstrom acts downstream of or in parallel to H3K9me3. Our work uncovers the widespread influence of transposons and the piRNA pathway on chromatin patterns and gene expression programs. RNA Polymerase II and H3K9me3 occupancy, and steady-state and nascent RNA levels in wild-type ovarian somatic cells (OSC) and RNAi knock-downs of the piRNA pathway components. RNA Polymerase II occupancy in tissue-specific knockdowns of tejas (control) and armi in somatic cells of Drosophila ovary.

ORGANISM(S): Drosophila melanogaster

SUBMITTER: Grzegorz Sienski

PROVIDER: E-GEOD-41729 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Publications

Transcriptional silencing of transposons by Piwi and maelstrom and its impact on chromatin state and gene expression.

Sienski Grzegorz G Dönertas Derya D Brennecke Julius J

Cell 20121115 5

Eukaryotic genomes are colonized by transposons whose uncontrolled activity causes genomic instability. The piRNA pathway silences transposons in animal gonads, yet how this is achieved molecularly remains controversial. Here, we show that the HMG protein Maelstrom is essential for Piwi-mediated silencing in Drosophila. Genome-wide assays revealed highly correlated changes in RNA polymerase II recruitment, nascent RNA output, and steady-state RNA levels of transposons upon loss of Piwi or Maelst ...[more]

PMID: 23159368

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Project description:PIWI-clade Argonaute proteins silence transposon expression in animal gonads. Their target specificity is defined by bound ~23-30nt piRNAs that are processed from single-stranded precursor transcripts via two distinct pathways. Primary piRNAs are defined by the endo-nuclease Zucchini, while biogenesis of secondary piRNAs depends on piRNA-guided transcript cleavage and results in piRNA amplification. Here, we analyze the inter-dependencies between these piRNA biogenesis pathways in the developing Drosophila ovary. We show that secondary piRNA-guided target slicing is the predominant mechanism that specifies transcripts—including those from piRNA clusters—as primary piRNA precursors and that defines the spectrum of Piwi-bound piRNAs in germline cells. Post-transcriptional silencing in the cytoplasm therefore enforces nuclear, transcriptional target silencing, which ensures the tight suppression of transposons during oogenesis. As target slicing also defines the nuclear piRNA pool during mouse spermatogenesis, our findings uncover an unexpected conceptual similarity between the mouse and fly piRNA pathways. To understand the hierarchical order of primary versus secondary piRNA biogenesis in Drosophila ovaries, we sequenced piRNAs bound to total-Piwi, germline-Piwi, Aubergine and Argonaute3 from ovaries of germline specific knockdowns of control, piwi, aub, ago3 single knockdowns and aub/ago3 double knockdowns. To determine changes in Transposable Element (TE) transcription or TE RNA steady state in perturbed piRNA pathway conditions, we performed Pol2-ChIP-sequencing and polyA bound RNA-sequencing from ovaries of multiple germline knockdown genotypes. We also sequenced genomic DNA from ovaries of control knockdowns to experimentally estimate the TE copy number in our genetic background. Finally, we used CAP-seq from germline specific Piwi depletions to identify the Transcriptional Start Sites (TSS) in TEs in a deregulated background. Replicates are labeled with R1, R2, R3, R4 where indicated.

Dataset Information

Transcriptional silencing of transposable elements by Piwi and its impact on chromatin and gene expression

Publications

Transcriptional silencing of transposons by Piwi and maelstrom and its impact on chromatin state and gene expression.

Similar Datasets

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