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      RNA-mediated epigenetic regulation of gene expression

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      Nature Reviews Genetics
      Springer Science and Business Media LLC

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          Abstract

          Diverse classes of RNA, ranging from small to long non-coding RNAs, have emerged as key regulators of gene expression, genome stability and defence against foreign genetic elements. Small RNAs modify chromatin structure and silence transcription by guiding Argonaute-containing complexes to complementary nascent RNA scaffolds and then mediating the recruitment of histone and DNA methyltransferases. In addition, recent advances suggest that chromatin-associated long non-coding RNA scaffolds also recruit chromatin-modifying complexes independently of small RNAs. These co-transcriptional silencing mechanisms form powerful RNA surveillance systems that detect and silence inappropriate transcription events, and provide a memory of these events via self-reinforcing epigenetic loops.

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          Most cited references108

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          RNA silencing in plants.

          There are at least three RNA silencing pathways for silencing specific genes in plants. In these pathways, silencing signals can be amplified and transmitted between cells, and may even be self-regulated by feedback mechanisms. Diverse biological roles of these pathways have been established, including defence against viruses, regulation of gene expression and the condensation of chromatin into heterochromatin. We are now in a good position to investigate the full extent of this functional diversity in genetic and epigenetic mechanisms of genome control.
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            Human Argonaute2 mediates RNA cleavage targeted by miRNAs and siRNAs.

            Argonaute proteins associate with small RNAs that guide mRNA degradation, translational repression, or a combination of both. The human Argonaute family has eight members, four of which (Ago1 through Ago4) are closely related and coexpressed in many cell types. To understand the biological function of the different Ago proteins, we set out to determine if Ago1 through Ago4 are associated with miRNAs as well as RISC activity in human cell lines. Our results suggest that miRNAs are incorporated indiscriminately of their sequence into Ago1 through Ago4 containing microRNPs (miRNPs). Purification of the FLAG/HA-epitope-tagged Ago containing complexes from different human cell lines revealed that endonuclease activity is exclusively associated with Ago2. Exogenously introduced siRNAs also associate with Ago2 for guiding target RNA cleavage. The specific role of Ago2 in guiding target RNA cleavage was confirmed independently by siRNA-based depletion of individual Ago members in combination with a sensitive positive-readout reporter assay.
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              RNA interference is mediated by 21- and 22-nucleotide RNAs.

              Double-stranded RNA (dsRNA) induces sequence-specific posttranscriptional gene silencing in many organisms by a process known as RNA interference (RNAi). Using a Drosophila in vitro system, we demonstrate that 21- and 22-nt RNA fragments are the sequence-specific mediators of RNAi. The short interfering RNAs (siRNAs) are generated by an RNase III-like processing reaction from long dsRNA. Chemically synthesized siRNA duplexes with overhanging 3' ends mediate efficient target RNA cleavage in the lysate, and the cleavage site is located near the center of the region spanned by the guiding siRNA. Furthermore, we provide evidence that the direction of dsRNA processing determines whether sense or antisense target RNA can be cleaved by the siRNA-protein complex.
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                Author and article information

                Journal
                Nature Reviews Genetics
                Nat Rev Genet
                Springer Science and Business Media LLC
                1471-0056
                1471-0064
                February 2015
                January 2 2015
                February 2015
                : 16
                : 2
                : 71-84
                Article
                10.1038/nrg3863
                4376354
                25554358
                fc3e69c1-d5a0-4075-8c09-f3eb88489438
                © 2015

                http://www.springer.com/tdm

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