Showing papers by "Amy E. Pasquinelli published in 2012"
TL;DR: This work has shown that targets can reciprocally control the level and function of miRNAs, and this has important implications for the use of these RNAs in therapeutic settings.
Abstract: MicroRNAs (miRNAs) have emerged as key gene regulators in diverse biological pathways. These small non-coding RNAs bind to target sequences in mRNAs, typically resulting in repressed gene expression. Several methods are now available for identifying miRNA target sites, but the mere presence of an miRNA-binding site is insufficient for predicting target regulation. Regulation of targets by miRNAs is subject to various levels of control, and recent developments have presented a new twist; targets can reciprocally control the level and function of miRNAs. This mutual regulation of miRNAs and target genes is challenging our understanding of the gene-regulatory role of miRNAs in vivo and has important implications for the use of these RNAs in therapeutic settings.
1,443 citations
TL;DR: This work found that the Argonaute protein in Caenorhabditis elegans, ALG-1, binds to a specific site at the 3′ end of let-7 miRNA primary transcripts and promotes downstream processing events, establishing a new mechanism for controlling miRNA expression.
Abstract: MicroRNAs (miRNAs) comprise a large family of small RNA molecules that post-transcriptionally regulate gene expression in many biological pathways. Most miRNAs are derived from long primary transcripts that undergo processing by Drosha to produce ~65-nucleotide precursors that are then cleaved by Dicer, resulting in the mature 22-nucleotide forms. Serving as guides in Argonaute protein complexes, mature miRNAs use imperfect base pairing to recognize sequences in messenger RNA transcripts, leading to translational repression and destabilization of the target messenger RNAs. Here we show that the miRNA complex also targets and regulates non-coding RNAs that serve as substrates for the miRNA-processing pathway. We found that the Argonaute protein in Caenorhabditis elegans, ALG-1, binds to a specific site at the 3′ end of let-7 miRNA primary transcripts and promotes downstream processing events. This interaction is mediated by mature let-7 miRNA through a conserved complementary site in its own primary transcript, thus creating a positive-feedback loop. We further show that ALG-1 associates with let-7 primary transcripts in nuclear fractions. Argonaute also binds let-7 primary transcripts in human cells, demonstrating that the miRNA pathway targets non-coding RNAs in addition to protein-coding messenger RNAs across species. Moreover, our studies in C. elegans reveal a novel role for Argonaute in promoting biogenesis of a targeted transcript, expanding the functions of the miRNA pathway in gene regulation. This discovery of autoregulation of let-7 biogenesis establishes a new mechanism for controlling miRNA expression.
218 citations
TL;DR: This review attempts to bring order to the small ncRNA transcriptome by covering some of the major milestones of recent years, and goes through many of the new properties that have been attributed to already familiar RNA molecules, and introduces some the more recent novel classes of tiny ncRNAs.
115 citations
TL;DR: One of the first characterized miRNAs, let-7, is reviewed and its role in development and the intricacies of its biogenesis and function are described.
Abstract: Noncoding RNAs have emerged as an integral part of posttranscriptional gene regulation Among that class of RNAs are the microRNAs (miRNAs), which posttranscriptionally regulate target mRNAs containing complementary sequences The broad presence of miRNAs in lower eukaryotes, plants, and mammals highlights their importance throughout evolution MiRNAs have been shown to regulate many pathways, including development, and disruption of miRNA function can lead to disease (Ivey and Srivastava, 2010; Jiang et al, 2009) Although the first miRNA genes were discovered in the nematode, Caenorhabditis elegans, almost 20 years ago, the field of miRNA research began when they were found in multiple organisms a little over a decade ago (Lagos-Quintana et al, 2001; Lau et al, 2001; Lee and Ambros, 2001; Lee et al, 1993; Pasquinelli et al, 2000; Wightman et al, 1993) Here, we review one of the first characterized miRNAs, let-7, and describe its role in development and the intricacies of its biogenesis and function
59 citations
TL;DR: The results reveal that miRNAs can broadly regulate other small RNA pathways and, thus, have far reaching effects on gene expression beyond directly targeting specific mRNAs.
Abstract: RNA interference (RNAi) utilizes small interfering RNAs (siRNAs) to direct silencing of specific genes through transcriptional and post-transcriptional mechanisms. The siRNA guides can originate from exogenous (exo–RNAi) or natural endogenous (endo–RNAi) sources of double-stranded RNA (dsRNA). In Caenorhabditis elegans, inactivation of genes that function in the endo–RNAi pathway can result in enhanced silencing of genes targeted by siRNAs from exogenous sources, indicating cross-regulation between the pathways. Here we show that members of another small RNA pathway, the mir-35-41 cluster of microRNAs (miRNAs) can regulate RNAi. In worms lacking miR-35-41, there is reduced expression of lin-35/Rb, the C. elegans homolog of the tumor suppressor Retinoblastoma gene, previously shown to regulate RNAi responsiveness. Genome-wide microarray analyses show that targets of endo–siRNAs are up-regulated in mir-35-41 mutants, a phenotype also displayed by lin-35/Rb mutants. Furthermore, overexpression of lin-35/Rb specifically rescues the RNAi hypersensitivity of mir-35-41 mutants. Although the mir-35-41 miRNAs appear to be exclusively expressed in germline and embryos, their effect on RNAi sensitivity is transmitted to multiple tissues and stages of development. Additionally, we demonstrate that maternal contribution of miR-35-41 or lin-35/Rb is sufficient to reduce RNAi effectiveness in progeny worms. Our results reveal that miRNAs can broadly regulate other small RNA pathways and, thus, have far reaching effects on gene expression beyond directly targeting specific mRNAs.
43 citations
TL;DR: A complex of PUF (named after founding members Pumilio and Fem-3 binding factor) and Argonaute proteins can stall translation elongation on bound mRNAs by interacting with eEF1A and inhibiting its GTPase activity.
Abstract: A complex of PUF (named after founding members Pumilio and Fem-3 binding factor) and Argonaute proteins can stall translation elongation on bound mRNAs by interacting with eEF1A and inhibiting its GTPase activity.
1 citations
TL;DR: An answer to the question of how histone 3′ ends are matured in worms is presented that, surprisingly, involves RNAi pathway factors.
Abstract: As the building blocks of chromatin, histones need to be synthesized efficiently and synchronously with DNA replication. The mRNAs encoding the core histones undergo a distinct 3′‐end formation pathway that results in mature mRNAs ending in a stem loop instead of a polyadenylated tail. Considering that the factors involved in histone 3′‐end processing are well conserved across Eukarya, the absence of some of these components in C. elegans draws the question of how histone 3′ ends are matured in worms. In this issue of The EMBO Journal , Avgousti et al (2012) present an answer that, surprisingly, involves RNAi pathway factors.
1 citations