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microRNAs : genome regulators. Aizhan Bizhanova. Overview. miRNA What are miRNAs ? Function and role C.elegans Role of miRNAs in developmental genetics of C.elegans lin-4 miRNA , “precocious” and “retarded” phenotypes Drosophila let-7 miRNA affects neuronal cell differentiation?.

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Presentation Transcript
  • miRNA
  • What are miRNAs?
  • Function and role
  • C.elegans
  • Role of miRNAs in developmental genetics of C.elegans
  • lin-4 miRNA, “precocious” and “retarded” phenotypes
  • Drosophila
  • let-7 miRNA affects neuronal cell differentiation?
  • microRNAs (miRNAs) are single-stranded non-coding RNAs, 21-23 nt long.
  • Discovered by 1993 by Victor Ambros, Rosalind Lee and Rhonda Feinbaum during a study of the gene lin-14 in C. elegansdevelopment
  • miRNAs regulate their target genes by base pairing with 3’ UTR of mRNA
  • 3’ Untranslated Region is a protein binding site in mRNA that is not translated
  • miRNAs bind with their “seed regions” (nucleotides 2-7) to the 3’ UTR of their target mRNA via base complementarity
making mirnas
Making miRNAs

1.Transcribing the primary miRNA (pri-miRNA)

  • RNA is capped and poly-adenylated
  • Specific stem-loop structures form

2. Nuclear processing of pri-miRNA

  • Drosha/Pasha complex cleaves out the base of the stem-loop structure, releasing the pre-miRNA

3. Export of pre-miRNA from the nucleus to the cytoplasm by Exportin5

4. Cytoplasmic processing of pre-miRNA

  • Dicer cleaves the “loop” portion to form the miRNA duplex

5.Loading of miRNA duplex into RISC

6.Strand selection

7.RISC activation

8.miRNA-RISC activity

mirnas role and function
miRNAs: role and function
  • Human genome has about 200-300 miRNA genes (1% of the protein coding genes)
  • Shared miRNA sites in different animal genomes- homologous miRNA putative targets?
  • Base pair with sites in the 3’ UTR of their target mRNAs. The seed sequence at the 5’ end of miRNA determines the specificity of miRNA-target RNA interactions.
  • Downregulate the expression of target proteins
  • Play an important role in development, cellular differentiation, proliferation, oncogenesis and apoptosis, etc.
mode of action of mirnas in plants and animals
Mode of Action of miRNAs in Plants and Animals


lin 4 the first discovered mi rna
lin-4: the first discovered miRNA
  • Heterochronic genes control developmental timing
  • lin-4miRNA is a heterochronic gene


  • lin-4


Vella and Slack, 2005

let 7 cell fate determinant
let-7 : cell fate “determinant”?



clockwork orange


  • Ecdysone?



Taken from Sokol, presentation

Zhu, 2006