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Encyclopedia > MiRNA


In genetics, a miRNA (micro-RNA) is a form of single-stranded RNA which is typically 20-25 nucleotides long, and is thought to regulate the expression of other genes. miRNAs are RNA genes which are transcribed from DNA, but are not translated into protein. The DNA sequence that codes for an miRNA gene is longer than the miRNA. This DNA sequence includes the miRNA sequence and an approximate reverse complement. When this DNA sequence is transcribed into a single-stranded RNA molecule, the miRNA sequence and its reverse-complement base pair to form a double stranded RNA hairpin loop; this forms a primary miRNA structure (pri-miRNA). In animals, the nuclear enzyme Drosha cleaves the base of the hairpin to form pre-miRNA. The pre-miRNA molecule is then actively transported out of the nucleus into the cytoplasm by Exportin 5, a carrier protein. The Dicer enzyme then cuts 20-25 nucleotides from the base of the hairpin to release the mature miRNA. In plants, which lack Drosha homologues, pri- and pre-miRNA processing by Dicer probably takes place in the nucleus, and mature miRNA duplexes are exported to the cytosol by Exportin 5. Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ... Ribonucleic acid (RNA) is a nucleic acid polymer consisting of covalently bound nucleotides. ... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... Gene expression, also called protein expression or often simply expression is the process by which a genes DNA sequence is converted into the structures and functions of a cell. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... It has been suggested that noncoding RNA be merged into this article or section. ... Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. Or, in other words, the transfer of genetic information from DNA into RNA. In the case of protein-encoding DNA, transcription is the beginning of the process that ultimately... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid —usually in the form of a double helix— that contains the genetic instructions specifying the biological development of all cellular forms of life, and most viruses. ... Translation in the cytoplasm; tRNA carries amino acids which are added to the growing peptide chain in the ribosome. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... In mathematics, a sequence is a list of objects (or events) arranged in a linear fashion, such that the order of the members is well defined and significant. ... Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. Or, in other words, the transfer of genetic information from DNA into RNA. In the case of protein-encoding DNA, transcription is the beginning of the process that ultimately... Ribonucleic acid (RNA) is a nucleic acid polymer consisting of covalently bound nucleotides. ... There are other meanings of hairpin In genetics, a hairpin is a part of single-stranded DNA, usually a palindromic sequence, that aligns with itself to form a needle-like structure. ... In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells and contains the nuclear genes which form most of the cells genetic material. ... Cytoplasm is like jelly-like material that fills cells. ... Dicer protein Dicer is an RNAse III nuclease which cuts dsRNA into siRNAs. ... Ribbon diagram of the enzyme TIM. TIM is catalytically perfect, meaning its conversion rate is limited, or nearly limited to its substrate diffusion rate. ... It has been suggested that Endonuclease be merged into this article or section. ...


The function of miRNAs appears to be in gene regulation. For that purpose, a miRNA is complementary to a part of one or more messenger RNAs (mRNAs). Animal miRNAs are usually complementary to a site in the 3' UTR whereas plant miRNAs are usually complementary to coding regions of mRNAs. The annealing of the miRNA to the mRNA then inhibits protein translation, but sometimes facilitates cleavage of the mRNA. This is thought to be the primary mode of action of plant miRNAs. In such cases, the formation of the double-stranded RNA through the binding of the miRNA triggers the degradation of the mRNA transcript through a process similar to RNA interference (RNAi), though in other cases it is believed that the miRNA complex blocks the protein translation machinery or otherwise prevents protein translation without causing the mRNA to be degraded. miRNAs may also target methylation of genomic sites which correspond to targeted mRNAs. miRNAs function in association with a complement of proteins collectively termed the miRNP. In genetics, a double-stranded DNA or RNA strand consists of two complementary strands of base pairs, which are non-covalently connected via two or three hydrogen bonds. ... The life cycle of an mRNA in a eukaryotic cell. ... In genetics, the 3 UTR (read as 3 prime untranslated region) is a particular section of messenger RNA (mRNA). ... RNA interference (RNAi) is a mechanism in molecular biology where the presence of certain fragments of double-stranded RNA (dsRNA) interferes with the expression of a particular gene which shares a homologous sequence with the dsRNA. Before RNAi was well characterized, it was called by other names, including post transcriptional... In biochemistry, methylation refers to the replacement of a hydrogen atom (H) with a methyl group (CH3), regardless of the substrate. ...


This effect was first described for the worm Caenorhabditis elegans in 1993 by R. C. Lee of Harvard University. As of 2002, miRNAs have been confirmed in various plants and animals, including C. elegans, human and the plant Arabidopsis thaliana. Genes have been found in bacteria that are similar in the sense that they control mRNA abundance or translation by binding an mRNA by base pairing, however they are not generally considered to be miRNAs because the Dicer enzyme is not involved. Binomial name Caenorhabditis elegans Maupas, 1900 Caenorhabditis elegans (pronounced see-no-rab-DYE-tis) is a free-living nematode (one of the roundworms), about 1 mm in length, which lives in a temperate soil environment. ... 1993 (MCMXCIII) was a common year starting on Friday of the Gregorian calendar and marked the Beginning of the International Decade to Combat Racism and Racial Discrimination (1993-2003). ... Harvard University campus (old map) Harvard University (incorporated as The President and Fellows of Harvard College) is a private university in Cambridge, Massachusetts. ... For album titles with the same name, see 2002 (album). ... Divisions Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants Adiantum pedatum (a fern... Phyla Subregnum Parazoa Porifera (sponges) Subregnum Agnotozoa Placozoa (trichoplax) Orthonectida (orthonectids) Rhombozoa (dicyemids) Subregnum Eumetazoa Radiata (unranked) (radial symmetry) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anemones) Bilateria (unranked) (bilateral symmetry) Acoelomorpha (basal) Orthonectida (parasitic to flatworms, echinoderms, etc. ... Trinomial name Homo sapiens sapiens Linnaeus, 1758 Humans, or human beings, are biologically classified as bipedal primates belonging to the mammalian species Homo sapiens (Latin for wise man or thinking man) under the family Hominidae (the great apes). ... Binomial name Arabidopsis thaliana (L.) Heynh. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ...


The term miRNA was first introduced in a set of three articles in Science (26 October 2001)[1] Science is the journal of the American Association for the Advancement of Science (AAAS). ... October 26 is the 299th day of the year (300th in leap years) in the Gregorian Calendar, with 66 days remaining. ... 2001: A Space Odyssey. ...


In plants, similar RNA species termed short-interfering RNAs siRNAs are used to prevent the transcription of viral RNA. While this siRNA is double-stranded, the mechanism seems to be closely related to that of miRNA, especially taking the hairpin structures into account. siRNAs are also used to regulate cellular genes, as miRNAs do. Small interfering RNA (siRNA) are a class of 20-25 nucleotide-long RNA molecules that interfere with the expression of genes. ... The human immunodeficiency virus (HIV) A bacteriophage virus A virus is a submicroscopic parasitic particle that infects cells in biological organisms. ...


The activity of an miRNA can be experimentally blocked using a locked nucleic acid oligo, a Morpholino oligo[2] or a 2'-O-methyl RNA oligo. [3]Most efficient methods for miRNA detection are based on oligonucleotides modified with locked nucleic acids.[4] A locked nucleic acid (LNA) is a modified RNA nucleotide. ... Morpholino oligos are an antisense technology used to block access of other molecules to specific sequences within nucleic acid molecules. ... A locked nucleic acid (LNA) is a modified RNA nucleotide. ...

Contents


miRNA and cancer

miRNA has been found to have links with some types of cancer. it is carsenogetic and is found is pens in pauls pencil case, toilet paper and tissues When normal cells are damaged beyond repair, they are eliminated by apoptosis. ...


A study of mice altered to produce excess c-myc — a protein implicated in several cancers — shows that miRNA has an effect on the development of cancer. Mice that were engineered to produce a surplus of types of miRNA found in lymphoma cells developed the disease within 50 days and died two weeks later. In contrast, mice without the surplus miRNA lived over 100 days.[5] c-Myc is a mammalian transcription factor belonging to the bHLH (basic Helix Loop Helix)_Leucine Zipper family. ... Lymphoma is a variety of cancer that originates in the lymphatic system. ...


Another study found that two types of miRNA inhibit the E2F1 protein, which regulates cell proliferation. miRNA appears to bind to messenger RNA before it can be translated to proteins that switch genes on and off.[6] The term cell growth is used in two different ways in biology. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ...


By measuring activity among 217 genes encoding miRNA, patterns of gene activity that can distinguish types of cancers can be discerned. miRNA signatures may enable classification of cancer. This will allow doctors to determine the original tissue type which spawned a cancer and to be able to target a treatment course based on the original tissue type. miRNA profiling has already been able to determine whether patients with chronic lymphocytic leukemia had slow growing or aggressive forms of the cancer.[7] Chronic lymphocytic leukemia (or chronic lymphoid leukemia) CLL, is a cancer in which too many lymphocytes (a type of white blood cells) are produced. ...


References

  1. ^ Ruvkun, G. (Oct 26 2001). "Molecular biology. Glimpses of a tiny RNA world.". Science 294 (5543): 797-9. PMID: 11679654.
  2. ^ Kloosterman, WP, Wienholds E, Ketting RF, Plasterk RH (Dec 7 2004). "Substrate requirements for let-7 function in the developing zebrafish embryo". Nucleic Acids Res. 32 (21): 6284-91. PMID: 15585662.
  3. ^ Meister, G, Landthaler M, Dorsett Y, Tuschl T (Mar 2004). "Sequence-specific inhibition of microRNA- and siRNA-induced RNA silencing". RNA 10 (3): 544-50. PMID: 14970398.
  4. ^ Kloosterman, WP, Wienholds E, de Bruijn E, Kauppinen S, Plasterk RH (Jan 2006). "In situ detection of miRNAs in animal embryos using LNA-modified oligonucleotide probes". Nat Methods (1): 27-9. PMID: 16369549.
  5. ^ He L, Thomson JM, Hemann MT, Hernando-Monge E, Mu D, Goodson S, Powers S, Cordon-Cardo C, Lowe SW, Hannon GJ, Hammond SM (2005). "A microRNA polycistron as a potential human oncogene". Nature 435 (7043): 828-833. PMID 15944707.
  6. ^ O'Donnell KA, Wentzel EA, Zeller KI, Dang CV, Mendell JT (2005). "c-Myc-regulated microRNAs modulate E2F1 expression". Nature 435 (7043): 839-843. PMID 15944709.
  7. ^ Lu J, Getz G, Miska EA, Alvarez-Saavedra E, Lamb J, Peck D, Sweet-Cordero A, Ebert BL, Mak RH, Ferrando AA, Downing JR, Jacks T, Horvitz HR, Golub TR (2005). "MicroRNA expression profiles classify human cancers". Nature 435 (7043): 834-838. PMID 15944708.
  • This paper defines miRNA and proposes guidelines to follow in classifying RNA genes as miRNA: Ambros V, Bartel B, Bartel DP, Burge CB, Carrington JC, Chen X, Dreyfuss G, Eddy SR, Griffiths-Jones S, Marshall M, Matzke M, Ruvkun G, Tuschl T (2003). "A uniform system for microRNA annotation". RNA 9 (3): 277-279. PMID 12592000.
  • This paper discusses the processes that miRNA and siRNAs are involved in, in the context of 2 articles in the same issue of the journal Science: Baulcombe D (2002). "DNA events. An RNA microcosm.". Science 297 (5589): 2002-2003. PMID 12242426.
  • This paper describes the discovery of lin-4, the first miRNA to be discovered (editor's note: in fact, no Wikipedia editor has yet read this paper, only made inferences from a citation): Lee RC, Feinbaum RL, Ambros V (1993). "The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14". Cell 75 (5): 843-854. PMID 8252621.

First title page, November 4, 1869 Nature is one of the oldest and most reputable scientific journals, first published on 4 November 1869. ... First title page, November 4, 1869 Nature is one of the oldest and most reputable scientific journals, first published on 4 November 1869. ... First title page, November 4, 1869 Nature is one of the oldest and most reputable scientific journals, first published on 4 November 1869. ... Science is the journal of the American Association for the Advancement of Science (AAAS). ...

See also

Small interfering RNA (siRNA) are a class of 20-25 nucleotide-long RNA molecules that interfere with the expression of genes. ... Gene expression, also called protein expression or often simply expression is the process by which a genes DNA sequence is converted into the structures and functions of a cell. ...

External links

  • Probabilistic prediction of microRNAs - ProMiR II
  • miRNA target prediction - miRacle
  • The miRNA Registry
  • TargetmiR Infobase of microRNA Targets
  • Papers from the Ambros lab on miRNAs
  • miRNA target prediction - RNAhybrid
  • miRNA target prediction - miRanda
  • miRNA target prediction - PicTar
  • miRNA target prediction - MicroInspector
Nucleic acids edit
Nucleobases: Adenine | Thymine | Uracil | Guanine | Cytosine | Purine | Pyrimidine
Nucleosides: Adenosine | Uridine | Guanosine | Cytidine | Deoxyadenosine | Thymidine | Deoxyguanosine | Deoxycytidine
Nucleotides: AMP | UMP | GMP | CMP | ADP | UDP | GDP | CDP | ATP | UTP | GTP | CTP | cAMP | cGMP
Deoxynucleotides: dAMP | dTMP | dGMP | dCMP | dADP | dTDP | dGDP | dCDP | dATP | dTTP | dGTP | dCTP
Nucleic acids: DNA | mtDNA | cDNA | GNA | RNA | mRNA | tRNA | rRNA | ncRNA | sgRNA | shRNA | siRNA | snRNA | miRNA | snoRNA | LNA | PNA | TNA | Oligonucleotide

  Results from FactBites:
 
MiRNA - Wikipedia, the free encyclopedia (965 words)
In genetics, a miRNA (micro-RNA) is a form of single-stranded RNA which is typically 20-25 nucleotides long, and is thought to regulate the expression of other genes.
The function of miRNAs appears to be in gene regulation.
Mice that were engineered to produce a surplus of types of miRNA found in lymphoma cells developed the disease within 50 days and died two weeks later.
MiRNA (488 words)
When this DNA sequence is transcribed into a single-stranded RNA molecule, the miRNA sequence and its reverse-complement base pair to form a double stranded RNA segment; overall this RNA structure is called a hairpin structure.
The annealing of the miRNA to the mRNA results in a double-stranded RNA, which is not transcribed into protein.
In either case, the miRNA prevents the protein biosynthesis of a specific gene, namely the one to whose mRNA it is complementary.
  More results at FactBites »

 
 

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