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Tailing and degradation of Argonaute-bound small RNAs protect the genome from uncontrolled RNAi

ABSTRACT: RNAi is a conserved mechanism in which small RNAs induce silencing of complementary targets. How Argonaute-bound small RNAs are targeted for degradation is not well understood. We show here that the adenyl-transferase Cid14, a member of the TRAMP complex, and the uridyl-transferase Cid16 add non-templated nucleotides to Argonaute-bound small RNAs in fission yeast. The tailing of Argonaute-bound small RNAs in vitro recruits the 3’-5’ exonuclease Rrp6 to degrade small RNAs. Failure in degradation of Argonaute-bound small RNAs results in accumulation of “noise” small RNAs on Argonaute and targeting of diverse euchromatic genes by RNAi. To protect themselves from uncontrolled RNAi, cid14Δ cells exploit the RNAi machinery and silence genes essential for RNAi itself, which is required for their viability. Our data indicate that surveillance of Argonaute-bound small RNAs by Cid14/Cid16 and the exosome protects the genome from uncontrolled RNAi and reveal a rapid RNAi-based adaptation to stress conditions.

ORGANISM(S): Schizosaccharomyces pombe

PROVIDER: GSE95821 | GEO | 2017/05/09

SECONDARY ACCESSION(S): PRJNA378525

REPOSITORIES: GEO

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TRAMP-mediated RNA surveillance prevents spurious entry of RNAs into the S. pombe siRNA pathway

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Project description:Tailing and degradation of Argonaute-bound small RNAs protect the genome from uncontrolled RNAi

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Argonaute and Trimmer generate Dicer-independent priRNAs and nucleate RNAi

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2014-04-21 | E-GEOD-38636 | biostudies-arrayexpress

Argonaute and Trimmer generate Dicer-independent priRNAs and nucleate RNAi

Project description:RNA interference is involved in silencing of transposable and repetitive elements. How these elements are initially recognized by RNAi is a fundamental and unanswered question. We previously identified a class of Dicer-independent small RNAs, called primal small RNAs (priRNAs), in fission yeast. The mechanism by which Dicer-independent small RNAs are generated is not clear for any species. Here we reconstitute priRNA biogenesis in vitro and demonstrate that priRNAs can nucleate RNAi in vivo. We identify 3'-5' exonuclease Trimmer and show that Argonaute, loaded with longer RNA precursors, recruits Trimmer to generate the new 3' end. Next, we show that antisense priRNAs accumulate in rrp6Δ cells and nucleate RNAi at subset of protein coding genes in a Trimmer- and priRNA-dependent manner. Thus, Rrp6-mediated degradation of antisense transcripts and priRNA precursors protects the genome from spurious RNAi. Our results suggest that Argonaute association with random RNA degradation products triggers RNAi in a process of transcriptome surveillance.

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Project description:Small RNAs regulate the genetic networks through a ribonucleoprotein complex called the RNA induced silencing complexes (RISC), which in mammals contains at its center one of four Argonaute proteins (Ago1-4). A key regulatory event in the RNAi and miRNA pathways is Ago loading, where double stranded small RNA duplexes are incorporated into RISC (pre-RISC) and then become single stranded (mature-RISC), a process that is not well understood. The Agos contain an evolutionary conserved PAZ (Piwi/Argonaute/Zwille) domain whose primary function is to bind the 3’-end of small RNAs. We created multiple Paz domain disrupted Ago mutant proteins and studied their biochemical properties and biological functionality in cells. We found that the Paz domain is dispensable for Ago loading of slicing-competent RISC. In contrast, in the absence of slicer activity or slicer substrate duplex RNAs, Paz-disrupted Agos bound duplex siRNAs but were unable to unwind/eject the passenger strand and form functional RISC complexes. We have discovered that the highly conserved Paz domain plays an important role in RISC activation, providing new mechanistic insights into how miRNAs regulate genes, as well as new insights for future design of miRNA and RNAi-based therapeutics. Various Argonautes associated small RNA profiles were generated by deep sequencing the Agos-IP samples in HEK293 Cells transfected with corresponding Argonaute.

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Germ granule association drives small RNA specificity for a nuclear Argonaute protein

Project description:RNA interference (RNAi) is a conserved gene silencing process that exists in diverse organisms to protect genome integrity and regulate gene expression. In C. elegans, the majority of RNAi pathway proteins localize to perinuclear, phase-separated germ granules, which are comprised of sub-domains referred to as P granules, Mutator foci, Z granules, and SIMR foci. However, the protein components and function of the newly discovered SIMR foci are unknown. Here we demonstrate that HRDE-2 localizes to SIMR foci and interacts with the germline nuclear RNAi Argonaute HRDE-1. Furthermore, HRDE-1 also localizes to SIMR foci, dependent on HRDE-2, but only in its small RNA unbound state. This germ granule localization is critical to promote the small RNA binding specificity of HRDE-1 and, in the absence of HRDE-2, HRDE-1 exclusively loads CSR-class 22G-RNAs rather than WAGO-class 22G-RNAs, resulting in H3K9me3 deposition on CSR-target genes. Thus, our study demonstrates that HRDE-2 is critical to ensure that the correct small RNAs are used to guide nuclear RNA silencing in the C. elegans germline.

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2014-09-23 | GSE61609 | GEO

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Project description:Argonaute proteins associate with small non-coding RNAs such as microRNAs, piRNAs and siRNAs to regulate gene expression required for cell proliferation and differentiation. Thse Argonaute proteins are the major components of effector complexes of non-coding RNA pathways. In C. elegans, we identified PPM-2, a Mg2+/Mn2+-dependent serine/threonine phosphatase, as a new regulator of the small RNA pathways in C. elegans. We demonstrate that PPM-2 is involved in the regulation of the let-7 microRNA family but also in the regulation of nuclear RNAi as well as it contributes to the expression of piRNAs. The loss of ppm-2 affects the expression level of Type 1 piRNAs and the stability of ALG-1, PRG-1 and NRDE-3 Argonaute proteins by sending them to the proteasomal degradation pathway. Altogether, our findings suggest that PPM-2 is regulating the function of small non-coding RNA pathways by preventing Argonaute proteins to be degraded via the proteasomal pathway.

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