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Small RNA World microRNAs(miRNAs)

Small RNA World microRNAs(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. siRNAs.

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Small RNA World microRNAs(miRNAs)

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  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 target’s 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

  6. 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

  7. 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

  8. 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

  9. 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?

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