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Small RNA World microRNAsmiRNAs
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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
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)
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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?
