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1.
Genes Dev ; 33(17-18): 1208-1220, 2019 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-31416967

RESUMO

The PIWI-interacting RNA (piRNA) pathway is a conserved small RNA-based immune system that protects animal germ cell genomes from the harmful effects of transposon mobilization. In Drosophila ovaries, most piRNAs originate from dual-strand clusters, which generate piRNAs from both genomic strands. Dual-strand clusters use noncanonical transcription mechanisms. Although transcribed by RNA polymerase II, cluster transcripts lack splicing signatures and poly(A) tails. mRNA processing is important for general mRNA export mediated by nuclear export factor 1 (Nxf1). Although UAP56, a component of the transcription and export complex, has been implicated in piRNA precursor export, it remains unknown how dual-strand cluster transcripts are specifically targeted for piRNA biogenesis by export from the nucleus to cytoplasmic processing centers. Here we report that dual-strand cluster transcript export requires CG13741/Bootlegger and the Drosophila nuclear export factor family protein Nxf3. Bootlegger is specifically recruited to piRNA clusters and in turn brings Nxf3. We found that Nxf3 specifically binds to piRNA precursors and is essential for their export to piRNA biogenesis sites, a process that is critical for germline transposon silencing. Our data shed light on how dual-strand clusters compensate for a lack of canonical features of mature mRNAs to be specifically exported via Nxf3, ensuring proper piRNA production.


Assuntos
Transporte Ativo do Núcleo Celular/genética , Proteínas de Drosophila/metabolismo , Drosophila/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteínas de Transporte Nucleocitoplasmático/metabolismo , Precursores de RNA/metabolismo , RNA Interferente Pequeno/metabolismo , Proteínas de Ligação a RNA/metabolismo , Animais , Elementos de DNA Transponíveis/genética , Drosophila/genética , Proteínas de Drosophila/genética , Peptídeos e Proteínas de Sinalização Intracelular/genética , Proteínas de Transporte Nucleocitoplasmático/genética , Proteínas de Ligação a RNA/genética
2.
Genes Dev ; 33(13-14): 844-856, 2019 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-31123065

RESUMO

The Piwi-interacting RNA (piRNA) pathway is a small RNA-based immune system that silences mobile genetic elements in animal germlines. piRNA biogenesis requires a specialized machinery that converts long single-stranded precursors into small RNAs of ∼25-nucleotides in length. This process involves factors that operate in two different subcellular compartments: the nuage/Yb body and mitochondria. How these two sites communicate to achieve accurate substrate selection and efficient processing remains unclear. Here, we investigate a previously uncharacterized piRNA biogenesis factor, Daedalus (Daed), that is located on the outer mitochondrial membrane. Daed is essential for Zucchini-mediated piRNA production and the correct localization of the indispensable piRNA biogenesis factor Armitage (Armi). We found that Gasz and Daed interact with each other and likely provide a mitochondrial "anchoring platform" to ensure that Armi is held in place, proximal to Zucchini, during piRNA processing. Our data suggest that Armi initially identifies piRNA precursors in nuage/Yb bodies in a manner that depends on Piwi and then moves to mitochondria to present precursors to the mitochondrial biogenesis machinery. These results represent a significant step in understanding a critical aspect of transposon silencing; namely, how RNAs are chosen to instruct the piRNA machinery in the nature of its silencing targets.


Assuntos
Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Mitocôndrias/metabolismo , RNA Helicases/metabolismo , RNA Interferente Pequeno/biossíntese , Animais , Linhagem Celular , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Técnicas de Silenciamento de Genes , Ligação Proteica , Transporte Proteico , RNA Interferente Pequeno/metabolismo
3.
Annu Rev Genet ; 52: 131-157, 2018 11 23.
Artigo em Inglês | MEDLINE | ID: mdl-30476449

RESUMO

PIWI-interacting RNAs (piRNAs) and their associated PIWI clade Argonaute proteins constitute the core of the piRNA pathway. In gonadal cells, this conserved pathway is crucial for genome defense, and its main function is to silence transposable elements. This is achieved through posttranscriptional and transcriptional gene silencing. Precursors that give rise to piRNAs require specialized transcription and transport machineries because piRNA biogenesis is a cytoplasmic process. The ping-pong cycle, a posttranscriptional silencing mechanism, combines the cleavage-dependent silencing of transposon RNAs with piRNA production. PIWI proteins also function in the nucleus, where they scan for nascent target transcripts with sequence complementarity, instructing transcriptional silencing and deposition of repressive chromatin marks at transposon loci. Although studies have revealed numerous factors that participate in each branch of the piRNA pathway, the precise molecular roles of these factors often remain unclear. In this review, we summarize our current understanding of the mechanisms involved in piRNA biogenesis and function.


Assuntos
Proteínas Argonautas/genética , Elementos de DNA Transponíveis/genética , RNA Interferente Pequeno/genética , Transcrição Gênica , Animais , Drosophila melanogaster/genética , Inativação Gênica , Gônadas/crescimento & desenvolvimento , RNA Interferente Pequeno/biossíntese
4.
bioRxiv ; 2024 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-38559194

RESUMO

In placental females, one copy of the two X chromosomes is largely silenced during a narrow developmental time window, in a process mediated by the non-coding RNA Xist1. Here, we demonstrate that Xist can initiate X-chromosome inactivation (XCI) well beyond early embryogenesis. By modifying its endogenous level, we show that Xist has the capacity to actively silence genes that escape XCI both in neuronal progenitor cells (NPCs) and in vivo, in mouse embryos. We also show that Xist plays a direct role in eliminating TAD-like structures associated with clusters of escapee genes on the inactive X chromosome, and that this is dependent on Xist's XCI initiation partner, SPEN2. We further demonstrate that Xist's function in suppressing gene expression of escapees and topological domain formation is reversible for up to seven days post-induction, but that sustained Xist up-regulation leads to progressively irreversible silencing and CpG island DNA methylation of facultative escapees. Thus, the distinctive transcriptional and regulatory topologies of the silenced X chromosome is actively, directly - and reversibly - controlled by Xist RNA throughout life.

5.
Elife ; 102021 02 04.
Artigo em Inglês | MEDLINE | ID: mdl-33538693

RESUMO

In animal gonads, the PIWI-interacting RNA (piRNA) pathway guards genome integrity in part through the co-transcriptional gene silencing of transposon insertions. In Drosophila ovaries, piRNA-loaded Piwi detects nascent transposon transcripts and instructs heterochromatin formation through the Panoramix-induced co-transcriptional silencing (PICTS) complex, containing Panoramix, Nxf2 and Nxt1. Here, we report that the highly conserved dynein light chain LC8/Cut-up (Ctp) is an essential component of the PICTS complex. Loss of Ctp results in transposon de-repression and a reduction in repressive chromatin marks specifically at transposon loci. In turn, Ctp can enforce transcriptional silencing when artificially recruited to RNA and DNA reporters. We show that Ctp drives dimerisation of the PICTS complex through its interaction with conserved motifs within Panoramix. Artificial dimerisation of Panoramix bypasses the necessity for its interaction with Ctp, demonstrating that conscription of a protein from a ubiquitous cellular machinery has fulfilled a fundamental requirement for a transposon silencing complex.


Assuntos
Elementos de DNA Transponíveis , Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Dineínas/genética , Inativação Gênica , Animais , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Dineínas/metabolismo
6.
Elife ; 82019 06 20.
Artigo em Inglês | MEDLINE | ID: mdl-31219034

RESUMO

The PIWI-interacting RNA (piRNA) pathway is a small RNA-based immune system that controls the expression of transposons and maintains genome integrity in animal gonads. In Drosophila, piRNA-guided silencing is achieved, in part, via co-transcriptional repression of transposons by Piwi. This depends on Panoramix (Panx); however, precisely how an RNA binding event silences transcription remains to be determined. Here we show that Nuclear Export Factor 2 (Nxf2) and its co-factor, Nxt1, form a complex with Panx and are required for co-transcriptional silencing of transposons in somatic and germline cells of the ovary. Tethering of Nxf2 or Nxt1 to RNA results in silencing of target loci and the concomitant accumulation of repressive chromatin marks. Nxf2 and Panx proteins are mutually required for proper localization and stability. We mapped the protein domains crucial for the Nxf2/Panx complex formation and show that the amino-terminal portion of Panx is sufficient to induce transcriptional silencing.


Assuntos
Inativação Gênica , Proteínas Nucleares/metabolismo , RNA Interferente Pequeno/metabolismo , Transcrição Gênica , Transporte Ativo do Núcleo Celular , Animais , Cromatina/metabolismo , Drosophila melanogaster/genética , Ligação Proteica , Estabilidade Proteica
7.
Nat Struct Mol Biol ; 25(9): 778-786, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-30104661

RESUMO

RNA viruses are a major threat to animals and plants. RNA interference (RNAi) and the interferon response provide innate antiviral defense against RNA viruses. Here, we performed a large-scale screen using Caenorhabditis elegans and its natural pathogen the Orsay virus (OrV), and we identified cde-1 as important for antiviral defense. CDE-1 is a homolog of the mammalian TUT4 and TUT7 terminal uridylyltransferases (collectively called TUT4(7)); its catalytic activity is required for its antiviral function. CDE-1 uridylates the 3' end of the OrV RNA genome and promotes its degradation in a manner independent of the RNAi pathway. Likewise, TUT4(7) enzymes uridylate influenza A virus (IAV) mRNAs in mammalian cells. Deletion of TUT4(7) leads to increased IAV mRNA and protein levels. Collectively, these data implicate 3'-terminal uridylation of viral RNAs as a conserved antiviral defense mechanism.


Assuntos
Caenorhabditis elegans/enzimologia , Caenorhabditis elegans/virologia , Imunidade Inata , RNA Nucleotidiltransferases/metabolismo , Vírus de RNA/metabolismo , Células A549 , Animais , Caenorhabditis elegans/genética , Humanos , Interferência de RNA , Vírus de RNA/imunologia , Vírus de RNA/fisiologia , RNA Viral/metabolismo , Transcriptoma , Replicação Viral
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