The Microprocessor complex mediates the genesis of microRNAs
TL;DR: In vivo knock-down and in vitro reconstitution studies revealed that both components of this smaller complex, termed Microprocessor, are necessary and sufficient in mediating the genesis of miRNAs from the primary miRNA transcript.
Abstract: MicroRNAs (miRNAs) are a growing family of small non-protein-coding regulatory genes that regulate the expression of homologous target-gene transcripts. They have been implicated in the control of cell death and proliferation in flies, haematopoietic lineage differentiation in mammals, neuronal patterning in nematodes and leaf and flower development in plants. miRNAs are processed by the RNA-mediated interference machinery. Drosha is an RNase III enzyme that was recently implicated in miRNA processing. Here we show that human Drosha is a component of two multi-protein complexes. The larger complex contains multiple classes of RNA-associated proteins including RNA helicases, proteins that bind double-stranded RNA, novel heterogeneous nuclear ribonucleoproteins and the Ewing's sarcoma family of proteins. The smaller complex is composed of Drosha and the double-stranded-RNA-binding protein, DGCR8, the product of a gene deleted in DiGeorge syndrome. In vivo knock-down and in vitro reconstitution studies revealed that both components of this smaller complex, termed Microprocessor, are necessary and sufficient in mediating the genesis of miRNAs from the primary miRNA transcript.
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TL;DR: I MicroRNAs (miRNAs) are an abundant class of small non-protein-coding RNAs that function as negative gene regulators as discussed by the authors, and have been shown to repress the expression of important cancer-related genes and might prove useful in the diagnosis and treatment of cancer.
Abstract: I MicroRNAs (miRNAs) are an abundant class of small non-protein-coding RNAs that function as negative gene regulators. They regulate diverse biological processes, and bioinformatic data indicates that each miRNA can control hundreds of gene targets, underscoring the potential influence of miRNAs on almost every genetic pathway. Recent evidence has shown that miRNA mutations or mis-expression correlate with various human cancers and indicates that miRNAs can function as tumour suppressors and oncogenes. miRNAs have been shown to repress the expression of important cancer-related genes and might prove useful in the diagnosis and treatment of cancer.
6,064 citations
TL;DR: Evidence has shown that miRNA mutations or mis-expression correlate with various human cancers and indicates that miRNAs can function as tumour suppressors and oncogenes.
Abstract: MicroRNAs (miRNAs) are an abundant class of small non-protein-coding RNAs that function as negative gene regulators They regulate diverse biological processes, and bioinformatic data indicates that each miRNA can control hundreds of gene targets, underscoring the potential influence of miRNAs on almost every genetic pathway Recent evidence has shown that miRNA mutations or mis-expression correlate with various human cancers and indicates that miRNAs can function as tumour suppressors and oncogenes miRNAs have been shown to repress the expression of important cancer-related genes and might prove useful in the diagnosis and treatment of cancer
5,693 citations
TL;DR: Small non-coding RNAs that function as guide molecules in RNA silencing are involved in nearly all developmental and pathological processes in animals and their dysregulation is associated with many human diseases.
Abstract: MicroRNAs (miRNAs) are small non-coding RNAs that function as guide molecules in RNA silencing. Targeting most protein-coding transcripts, miRNAs are involved in nearly all developmental and pathological processes in animals. The biogenesis of miRNAs is under tight temporal and spatial control, and their dysregulation is associated with many human diseases, particularly cancer. In animals, miRNAs are ∼22 nucleotides in length, and they are produced by two RNase III proteins--Drosha and Dicer. miRNA biogenesis is regulated at multiple levels, including at the level of miRNA transcription; its processing by Drosha and Dicer in the nucleus and cytoplasm, respectively; its modification by RNA editing, RNA methylation, uridylation and adenylation; Argonaute loading; and RNA decay. Non-canonical pathways for miRNA biogenesis, including those that are independent of Drosha or Dicer, are also emerging.
4,256 citations
TL;DR: This work has shown that the regulation of miRNA metabolism and function by a range of mechanisms involving numerous protein–protein and protein–RNA interactions has an important role in the context-specific functions of miRNAs.
Abstract: MicroRNAs (miRNAs) are a large family of post-transcriptional regulators of gene expression that are ~21 nucleotides in length and control many developmental and cellular processes in eukaryotic organisms. Research during the past decade has identified major factors participating in miRNA biogenesis and has established basic principles of miRNA function. More recently, it has become apparent that miRNA regulators themselves are subject to sophisticated control. Many reports over the past few years have reported the regulation of miRNA metabolism and function by a range of mechanisms involving numerous protein-protein and protein-RNA interactions. Such regulation has an important role in the context-specific functions of miRNAs.
4,123 citations
Cites background from "The Microprocessor complex mediates..."
...Keeping the Drosha to DGCR8 ratio in check may be important, as a threefold excess of DGCR8 dramatically inhibits Drosha processing activity in vitro...
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TL;DR: A role is proposed for miR-146 in control of Toll-like receptor and cytokine signaling through a negative feedback regulation loop involving down-regulation of IL-1 receptor-associated kinase 1 and TNF receptor- associated factor 6 protein levels.
Abstract: Activation of mammalian innate and acquired immune responses must be tightly regulated by elaborate mechanisms to control their onset and termination. MicroRNAs have been implicated as negative regulators controlling diverse biological processes at the level of posttranscriptional repression. Expression profiling of 200 microRNAs in human monocytes revealed that several of them (miR-146a/b, miR-132, and miR-155) are endotoxin-responsive genes. Analysis of miR-146a and miR-146b gene expression unveiled a pattern of induction in response to a variety of microbial components and proinflammatory cytokines. By means of promoter analysis, miR-146a was found to be a NF-κB-dependent gene. Importantly, miR-146a/b were predicted to base-pair with sequences in the 3′ UTRs of the TNF receptor-associated factor 6 and IL-1 receptor-associated kinase 1 genes, and we found that these UTRs inhibit expression of a linked reporter gene. These genes encode two key adapter molecules downstream of Toll-like and cytokine receptors. Thus, we propose a role for miR-146 in control of Toll-like receptor and cytokine signaling through a negative feedback regulation loop involving down-regulation of IL-1 receptor-associated kinase 1 and TNF receptor-associated factor 6 protein levels.
3,947 citations
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TL;DR: The two RNase III proteins, Drosha and Dicer, may collaborate in the stepwise processing of miRNAs, and have key roles in miRNA-mediated gene regulation in processes such as development and differentiation.
Abstract: Hundreds of small RNAs of approximately 22 nucleotides, collectively named microRNAs (miRNAs), have been discovered recently in animals and plants. Although their functions are being unravelled, their mechanism of biogenesis remains poorly understood. miRNAs are transcribed as long primary transcripts (pri-miRNAs) whose maturation occurs through sequential processing events: the nuclear processing of the pri-miRNAs into stem-loop precursors of approximately 70 nucleotides (pre-miRNAs), and the cytoplasmic processing of pre-miRNAs into mature miRNAs. Dicer, a member of the RNase III superfamily of bidentate nucleases, mediates the latter step, whereas the processing enzyme for the former step is unknown. Here we identify another RNase III, human Drosha, as the core nuclease that executes the initiation step of miRNA processing in the nucleus. Immunopurified Drosha cleaved pri-miRNA to release pre-miRNA in vitro. Furthermore, RNA interference of Drosha resulted in the strong accumulation of pri-miRNA and the reduction of pre-miRNA and mature miRNA in vivo. Thus, the two RNase III proteins, Drosha and Dicer, may collaborate in the stepwise processing of miRNAs, and have key roles in miRNA-mediated gene regulation in processes such as development and differentiation.
5,191 citations
"The Microprocessor complex mediates..." refers background in this paper
...This processing event is mediated by an RNase III endonuclease, Drosha, which cleaves both strands of the stem at sites near the base of the primary stem loo...
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TL;DR: It is shown that many 21- and 22-nt expressed RNAs, termed microRNAs, exist in invertebrates and vertebrates and that some of these novel RNAs are highly conserved, which suggests that sequence-specific, posttranscriptional regulatory mechanisms mediated by smallRNAs are more general than previously appreciated.
Abstract: In Caenorhabditis elegans, lin-4 and let-7 encode 22- and 21-nucleotide (nt) RNAs, respectively, which function as key regulators of developmental timing. Because the appearance of these short RNAs is regulated during development, they are also referred to as small temporal RNAs (stRNAs). We show that many 21- and 22-nt expressed RNAs, termed microRNAs, exist in invertebrates and vertebrates and that some of these novel RNAs, similar to let-7 stRNA, are highly conserved. This suggests that sequence-specific, posttranscriptional regulatory mechanisms mediated by small RNAs are more general than previously appreciated.
4,484 citations
"The Microprocessor complex mediates..." refers background in this paper
...It was recently suggested that most miRNA genes originate from independent transcription unit...
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TL;DR: Two small temporal RNAs, lin-4 andlet-7, control developmental timing in Caenorhabditis elegans and are found to be members of a large class of 21- to 24-nucleotide noncodingRNAs, called microRNAs (miRNAs), which imply that, as a class, miRNAs have broad regulatory functions in animals.
Abstract: Two small temporal RNAs (stRNAs), lin-4 and let-7, control developmental timing in Caenorhabditis elegans. We find that these two regulatory RNAs are members of a large class of 21- to 24-nucleotide noncoding RNAs, called microRNAs (miRNAs). We report on 55 previously unknown miRNAs in C. elegans. The miRNAs have diverse expression patterns during development: a let-7 paralog is temporally coexpressed with let-7; miRNAs encoded in a single genomic cluster are coexpressed during embryogenesis; and still other miRNAs are expressed constitutively throughout development. Potential orthologs of several of these miRNA genes were identified in Drosophila and human genomes. The abundance of these tiny RNAs, their expression patterns, and their evolutionary conservation imply that, as a class, miRNAs have broad regulatory functions in animals.
3,539 citations
"The Microprocessor complex mediates..." refers background in this paper
...It was recently suggested that most miRNA genes originate from independent transcription unit...
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TL;DR: The results indicate that microRNAs are components of the molecular circuitry that controls mouse hematopoiesis and suggest that other micro RNAs have similar regulatory roles during other facets of vertebrate development.
Abstract: MicroRNAs (miRNAs) are an abundant class of ∼22-nucleotide regulatory RNAs found in plants and animals. Some miRNAs of plants, Caenorhabditis elegans, and Drosophila play important gene-regulatory roles during development by pairing to target mRNAs to specify posttranscriptional repression of these messages. We identify three miRNAs that are specifically expressed in hematopoietic cells and show that their expression is dynamically regulated during early hematopoiesis and lineage commitment. One of these miRNAs, miR-181, was preferentially expressed in the B-lymphoid cells of mouse bone marrow, and its ectopic expression in hematopoietic stem/progenitor cells led to an increased fraction of B-lineage cells in both tissue-culture differentiation assays and adult mice. Our results indicate that microRNAs are components of the molecular circuitry that controls mouse hematopoiesis and suggest that other microRNAs have similar regulatory roles during other facets of vertebrate development.
3,307 citations
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TL;DR: Using bioinformatics and cDNA cloning, this work found 15 new miRNA genes in C. elegans that express small transcripts that vary in abundance during larval development, and three of them have apparent homologs in mammals and/or insects.
Abstract: The lin-4 and let-7 antisense RNAs are temporal regulators that control the timing of developmental events in Caenorhabditis elegans by inhibiting translation of target mRNAs. let-7 RNA is conserved among bilaterian animals, suggesting that this class of small RNAs [microRNAs (miRNAs)] is evolutionarily ancient. Using bioinformatics and cDNA cloning, we found 15 new miRNA genes in C. elegans. Several of these genes express small transcripts that vary in abundance during C. elegans larval development, and three of them have apparent homologs in mammals and/or insects. Small noncoding RNAs of the miRNA class appear to be numerous and diverse.
3,062 citations
"The Microprocessor complex mediates..." refers background in this paper
...It was recently suggested that most miRNA genes originate from independent transcription unit...
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