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Micro rn as gene silencing prez


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Micro rn as gene silencing prez

  1. 1. MicroRNAs (miRNAs) form a large class of ncRNAs function in repression of gene expression in Eukaryotes By recognizing short stretches of nucleotides within the , untranslated regions of mRNAs miRNAs recruit partner proteins to individual transcripts, leading to mRNA cleavage or hindering of translation
  2. 2. Mainly involved in PTGS Undergo complex biogenesis, ending in loading of a s.s 19–23 nucleotide sequence in miRNP or RISC In RISC, miRNAs serve as probes for recognizing nucleotide sequences on target RNAs Resulting in either arrest of translation or mRNA cleavage and degradation Gene silencing achieved in this manner is called the RNA (interference (RNAi
  3. 3. Located in introns of protein-coding genes and in both introns and exons of non-protein-coding genes In the nucleus, primiRNAs cleaved by a type III RNase called Drosha and its d.s RNA-binding protein co-factor named DGCR8 also called Pasha Alternatively, a subclass of pre-miRNAs is produced directly from introns (termed mirtrons) of mRNA precursors by splicing Pre-miRNAs are actively transported to cytoplasm by a nuclear membrane protein complex exportin-5/RanGTPase
  4. 4. In the cytoplasm, the loop of pre-miRNA is cleaved off by another RNase III called Dicer The resulting RNA duplex consists of a functional miRNA ( guide strand) retained by an Ago protein and a passenger *(strand (denoted as miRNA Ago-bound miRNA constitutes the basis of miRNA–protein effector complex miRNP or RISC Within RISC, miRNA serves as an adaptor for orienting and fastening specific mRNAs
  5. 5. (miRNAs bind to specific miRNA recognition elements (MREs Complementarity between MREs and miRNAs differ from plants to animals The extent of miRNA–MRE complementarity is directing the way a gene is silenced miRNAs with seed region base pairing to mRNA targets, cause gene silencing through interfering with translation or causing mRNA decay rather than endonucleolytic mRNA cleavage Non-cleavage repression and seems to proceed by a number of distinct mechanisms
  6. 6. A) Competition for the 5′-cap) structure by Ago protein of the RISC complex B) Inhibition of mRNA) circularization through deadenylation
  7. 7. C) Inhibition of ribosomal) subunit joining by Ago protein D) Premature ribosome drop-off) )dissociation of ribosomes)
  8. 8. E) Co-translational protein) degradation F) mRNA decay, accelerated by) deadenylation and decapping
  9. 9. G) mRNA sequestration into processing bodies)
  10. 10. miRNAs control developmental timing spatiotemporal expression of LIN-14 protein (encoded by lin-14 gene) in C. elegans miRNAs control tissue patterning/segmentation lsy-6 and miR-273, identified in C. elegans miRNAs control cellular proliferation and differentiation miR-290 cluster in embryonic stem (ES) cells miRNAs control diverse physiological processes let-7b, miR-375, and miR-124 all regulate insulin secretion , liver-specific miR-122 has been linked to cholesterol metabolism
  11. 11. Endogenous miRNAs can be suppressed using decoy targets (antagomirs or AMOs (anti-miRNA oligonucleotides synthetic antisense oligonucleotides ,which efficiently compete with endogenous mRNA targets for binding to specific miRNAs microRNA sponges miRNA sponges are artificial mRNA targets with multiple miRNA binding sites engineered into the 3′ UTRs
  12. 12. To enhance gene silencing elicited by a certain miRNA enzymatically generated or chemically synthesized miRNAs can be introduced into cells for longer lasting effects, expression of recombinant miRNAs from plasmids or viral vectors is a better option Combining the miRNA-based targeting with tissue-specific promoters is an effective strategy of preventing offtarget transgene expression