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Cues from mRNA splicing prevent default Argonaute silencing in C. elegans.

ABSTRACT: In animals, Argonaute small-RNA pathways scan germline transcripts to silence self-replicating genetic elements. However, little is known about how endogenous gene expression is recognized and licensed. Here, we show that the presence of introns and, by inference, the process of mRNA splicing prevents default Argonaute-mediated silencing in the C. elegans germline. The silencing of intronless genes is initiated independently of the piRNA pathway but nevertheless engages multiple components of the downstream amplification and maintenance mechanisms that mediate transgenerational silencing, including both nuclear and cytoplasmic members of the worm-specific Argonaute gene family (WAGOs). Small RNAs amplified from intronless mRNAs can trans-silence cognate intron-containing genes. Interestingly, a second, small RNA-independent cis-acting mode of silencing also acts on intronless mRNAs. Our findings suggest that cues put in place during mRNA splicing license germline gene expression and provide evidence for a splicing-dependent and dsRNA- and piRNA-independent mechanism that can program Argonaute silencing.

SUBMITTER: Makeyeva YV

PROVIDER: S-EPMC8693449 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Cues from mRNA splicing prevent default Argonaute silencing in C. elegans

Project description:In animals Argonaute small-RNA pathways scan germline transcripts to silence self-replicating genetic elements. Little is known however about how endogenous gene expression is recognized and licensed. Here we show that the presence of introns and by inference the process of mRNA splicing prevents default Argonaute-mediated silencing in the C. elegans germline. Silencing of intronless genes is initiated independently of the piRNA pathway but nevertheless engages multiple components of the downstream amplification and maintenance mechanisms that mediate transgenerational silencing including both nuclear and cytoplasmic members of the worm-specific Argonaute gene family (WAGOs). Small RNAs amplified from intronless mRNAs can trans-silence cognate intron-containing genes. Interestingly, a second small RNA-independent cis-acting mode of silencing also acts on intronless mRNAs. Our findings suggest that cues put in place during mRNA splicing license germline gene expression and provide evidence for a splicing-dependent and dsRNA- and piRNA-independent mechanism that can program Argonaute silencing.

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Cues from mRNA splicing prevent default Argonaute silencing in C. elegans

Project description:Cues from mRNA splicing prevent default Argonaute silencing in C. elegans

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HDAC1 SUMOylation promotes Argonaute-directed transcriptional silencing in <i>C. elegans</i>.

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The C. elegans CSR-1 argonaute pathway counteracts epigenetic silencing to promote germline gene expression.

Project description:Organisms can develop adaptive sequence-specific immunity by reexpressing pathogen-specific small RNAs that guide gene silencing. For example, the C. elegans PIWI-Argonaute/piwi-interacting RNA (piRNA) pathway recruits RNA-dependent RNA polymerase (RdRP) to foreign sequences to amplify a transgenerational small-RNA-induced epigenetic silencing signal (termed RNAe). Here, we provide evidence that, in addition to an adaptive memory of silenced sequences, C. elegans can also develop an opposing adaptive memory of expressed/self-mRNAs. We refer to this mechanism, which can prevent or reverse RNAe, as RNA-induced epigenetic gene activation (RNAa). We show that CSR-1, which engages RdRP-amplified small RNAs complementary to germline-expressed mRNAs, is required for RNAa. We show that a transgene with RNAa activity also exhibits accumulation of cognate CSR-1 small RNAs. Our findings suggest that C. elegans adaptively acquires and maintains a transgenerational CSR-1 memory that recognizes and protects self-mRNAs, allowing piRNAs to recognize foreign sequences innately, without the need for prior exposure

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A family of C. elegans VASA homologs control Argonaute pathway specificity and promote transgenerational silencing.

Project description:Germline Argonautes direct transcriptome surveillance within perinuclear membraneless organelles called nuage. In C. elegans, a family of Vasa-related Germ Line Helicase (GLH) proteins localize in and promote the formation of nuage. Previous studies have implicated GLH proteins in inherited silencing, but direct roles in small-RNA production, Argonaute binding, or mRNA targeting have not been identified. Here we show that GLH proteins compete with each other to control Argonaute pathway specificity, bind directly to Argonaute target mRNAs, and promote the amplification of small RNAs required for transgenerational inheritance. We show that the ATPase cycle of GLH-1 regulates direct binding to the Argonaute WAGO-1, which engages amplified small RNAs. Our findings support a dynamic and direct role for GLH proteins in inherited silencing beyond their role as structural components of nuage.

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Argonaute proteins couple chromatin silencing to alternative splicing

Project description:This SuperSeries is composed of the following subset Series: GSE39746: Argonaute proteins couple chromatin silencing to alternative splicing (exon array) GSE39748: Argonaute proteins couple chromatin silencing to alternative splicing (RNA IP-Seq) Refer to individual Series

2012-08-22 | E-GEOD-39749 | biostudies-arrayexpress

Argonaute proteins couple chromatin silencing to alternative splicing

Project description:This SuperSeries is composed of the SubSeries listed below.

2012-08-22 | GSE39749 | GEO

Argonaute proteins couple chromatin silencing to alternative splicing (exon array)

Project description:While Argonaute (AGO) proteins play a major role in transcriptional gene silencing (TGS) in many organisms, their role in the nucleus of somatic mammalian cells remains elusive. Here, we have purified AGO1 and AGO2 chromatin-embedded complexes, and found these proteins associated with previously described partners, but also with chromatin modifiers and, rather unexpectedly, with different splicing factors. Using the CD44 gene as a model for alternative splicing, we show that both AGO1 and AGO2 are required for Protein Kinase C (PKC)-dependent variant exon inclusion. AGO proteins facilitate the spliceosome recruitment and modulate the elongation rate of RNA polymerase II (RNAPII). The recruitment of AGO proteins to CD44 transcribed region is dependent on both the endonuclease Dicer and the chromodomain-containing protein HP1g, and results in locally increased levels of histone H3 lysine 9 (H3K9) methylation on variant exons. Genome wide analysis of splicing in either AGO2 or Dicer null cells showed that the two proteins have similar effects on many splicing events. Finally, sRNAs associated with nuclear AGO2 are mostly in sense orientation relative to protein-coding genes, supporting a role for intragenic antisense non-coding RNAs in the recruitment AGO and splicing factors. Together, our data demonstrate for the first time that the endogenous RNAi pathway is involved in alternative splicing decisions, unravelling a new model in which AGO proteins couple RNAPII elongation and chromatin modification. Study of AGO2 or Dicer knock-out on gene expression and splicing regulation in MEF cells Transcriptome analysis of AGO2 and Dicer null MEF cells on GeneChipM-BM-. Mouse Exon 1.0 ST Arrays (Affymetrix). Dicer null MEF cells and wild-type MEF cells were from M. Otsuka. AGO2 null MEF cells were from A. Tarakhovsky. Experiment has been done in experimental triplicates. 9 Total samples were analyzed.

2012-09-10 | E-GEOD-39746 | biostudies-arrayexpress

The Exon Junction Complex and intron removal prevent re-splicing of mRNA.

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Project description:Nearly every cell in the human body contains a set of programmable gene-silencing proteins named Argonaute. Argonaute proteins mediate gene regulation by small RNAs and thereby contribute to cellular homeostasis during diverse physiological process, such as stem cell maintenance, fertilization, and heart development. Over the last decade, remarkable progress has been made toward understanding Argonaute proteins, small RNAs, and their roles in eukaryotic biology. Here, we review current understanding of Argonaute proteins from a structural prospective and discuss unanswered questions surrounding this fascinating class of enzymes.

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