Small RNA World microRNAsmiRNAs

1
Small RNA WorldmicroRNAs(miRNAs)

• ECES458
• FALL 2001
• Student Kai He
• Instructor Dr. Sahinalp

2
imRNAs A New Class of Small RNA Molecules

• siRNAs small interfering RNAs
• stRNAs small temporal RNAs

3
siRNAs

• 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

4
stRNAs

• 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)

5
Dicer

• 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
  silencing

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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

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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 -
  miRNAs

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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

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Problems

• 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?