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Small RNA World microRNAsmiRNAs


imRNAs: A New Class of Small RNA Molecules. siRNAs: small interfering RNAs ... Expression pattern: varied and some were expressed in all cells and at all ... – PowerPoint PPT presentation

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Title: Small RNA World microRNAsmiRNAs

Small RNA WorldmicroRNAs(miRNAs)
  • ECES458
  • FALL 2001
  • Student Kai He
  • Instructor Dr. Sahinalp

imRNAs A New Class of Small RNA Molecules
  • siRNAs small interfering RNAs
  • stRNAs small temporal RNAs

  • Small interfering RNAs that have an integral role
    in the phenomenon of RNA interference(RNAi), a
    form of post-transcriptional gene silencing
  • RNAi 22 nt fragments, which bind to the
    complementary portion of the target mRNA and tag
    it for degradation
  • siRNA a role in conferring resistance and in
    preventing transcription

  • Small RNAs refer to small temporal RNAs
  • Including 22 nt, such as lin-4 and let-7 RNAs
  • Role the temporal regulation of Caenorhabditits
    elegans development, preventing translation of
    their target mRNAs by binding to the targets
    complementary 3 untranslated regions(UTRs)
  • From 70 nt ssRNA(single-stranded RNA)

  • A RNaseIII, which cleaves double-stranded RNA
    into discrete sizes
  • Involving generate siRNA
  • Dicer homologs exist in many organisms including
    C.elegans, yeast and humans
  • Roles cause defeats in development and gene

Small RNA Molecules
  • Found in
  • Drosophila
  • C.elegans
  • Hela cells
  • Genes
  • Lin-4
  • Let-7
  • Structures
  • Precursor RNA is folded into stem-loop
  • Roles
  • Regulate translation
  • Modify mRNA stability

Identifying miRNA
  • Using biochemical and bioinformatics approaches
  • Using Dicer to produce siRNA and stRNA, and
    obtain 22 nt with 5 phosphate region and 3
    hydroxy region
  • mRNAs, tRNAs, or rRNAs degradation products -

Charateristics of miRNAs
  • Found More than 100 new miRNAs
  • From Drosophila, C.elegans, Hela cells and so on
  • Conservation 15 of these miRNAs were conserved
    with 1-2 mismatched across worm, fly, and
    mammalian genomes
  • Location located at either the 3 or 5 region
    of a stem-loop within 70 nt RNA precursor
  • Expression pattern varied and some were
    expressed in all cells and at all developmental
    stages and others had a more restricted spatial
    and temporal expression pattern
  • Suggestions
  • miRNA might be involved in post-transcriptional
    regulation of developmental genes

  • Now we are not able to identify the miRNA targets
    by using an informatics approaches
  • Why maybe the entire miRNA does not have to be
    complementary to the target in order for binding
    to occur
  • Questions
  • What do these miRNAs do?
  • Are they involved in post-transcriptional gene
    regulation, if so, what are their target genes?
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