RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression, typically by causing the destruction of specific mRNA molecules. Two types of small ribonucleic acid (RNA) molecules – microRNA (miRNA) and small interfering RNA (siRNA) – are central to RNA interference.

1. DONE BY: HADIAH BASSAM AL MAHDI
M A S T E R O F S C I E N C E
G E N E T I C S D E P A R T M E N T , F A C U L T Y O F S C I E N C E
RNA INTERFERENCE

2. OUTLINE
 Introduction
 RNA silencing
 Definition of RNA interference
 Discovery of RNAi
 Mechanism of RNA interference
 siRNA
 miRNA
 Expolotion of RNA interference
 Conclusion

3. INTRODUCTION

4. RNA silencing
Several terms are used to describe RNA silencing;
usually there are three phenotypically different but
mechanistically similar phenomena:
1. post-trascriptional gene silencing (PTGS) in plants
2. Quelling in fungi
3. RNA interference in animal kingdom

5. Definition
RNA interference (RNAi) is a mechanism
that inhibits gene expression at the stage
of translation or by hindering the
transcription of specific genes.

6. Why do we need for interference ?
 Defense Mechanism
 Defense against Infection by viruses, etc
 As a defense mechanism to protect against transposons and
other insertional elements
 Genome Wide Regulation
 RNAi plays a role in regulating development and genome
maintenance.
 30% of human genome regulated

7. Discovery Of RNAi
 Making petonia flower with deeper purple color by
inserting extra copies of the gene into cell resulted in
paler flowers
 Inserting antisense RNA of par-1 gene to block it action
 The sense RNA which was used as control did the same job
 RNA from other genes did not affect par-1 gene
 2006 Nobel prize for the discovery that it is the dsRNA
(caused by contamination) which
blocked the transcription

8. MECHANISIM OF RNAi

9. RNAi Mechanism
 RNA interference (RNAi) acts in 3 ways:
1. Inhibit transcription by silencing the gene
2. Inhibit translation of mRNA
3. Destruct mRNA

10. where do these RNAi come from?
 Small interfering
RNA (siRNA) are
made from dsRNA
precursors
 microRNA (miRNA)
are encoded by genes

11. In Interference
 RNA
 siRNA: dsRNA 21-22 nt.
 miRNA: ssRNA 19-25nt. Encoded by non protein coding
genome
 RISC:
 RNA induced Silencing Complex, that cleaves mRNA
 The catalytic component of the RISC complex
include Argonaute
 Enzymes
 Dicer : produces 20-21 nt cleavages that initiate RNAi
 Drosha : cleaves base hairpin in to form pre miRNA; which is
later processed by Dicer

12. The mechanism of siRNA :
 Long dsRNA .
Dicer
 siRNA into two single-
stranded RNAs (ssRNAs)
 Guide (siRNA) enters the cell.
RISC + Argonaute
 Single stranded siRNA binds
to its target mRNA.
 The mRNA is now cut and
recognized as abnormal by the
cell.

13. Synthesis of miRNA
Gene encoding miRNA (nucleus)
(transcription)
Pri-miRNA
(Drosha)
Pre-miRNA (get out to cytoplasm)
(Dicer)
Mature-miRNA
 (RISC)
miRNA binds to its target mRNA
and Degraded

14. • Drosha cuts 11 bp away from dsRNA-ssRNA
junction
• Dicer is needed to generatemature miRNA from
pre-miRNA

15. miRNA siRNA
 Precursor: 70 nt shRNA
 Imperfect pairing required
 Function: mRNA cleavage
 Nearly conserved
 Encoded by own genes
(endogenous source )
 Precursor: Long dsRNA
 perfect pairing required
 Function: mRNA cleavage
 Not conserved
 Encoded by transposon or
viruses (exogenous source)
miRNA vs siRNA

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17. Expolotion OF RNAi

18. Expolotion of RNAi
 Protection against transposons & viruses
 Faster identification of gene function
 Role in regulating gene translation
 Role in cancer pathogenesis
 Agriculture

19. Protection against transposons & viruses
 45% of human genome is DNA originated from
transposons
 RNAi machinery silence transposons by recruiting
histone modifiers
 Mutations affecting RNAi machinery could reactivate
transposons
 RNAi machinery Silencing genes in HIV
 Silence the main structural protein in the virus, p24, and the
human protein CD4.
 Hit the virus where it counts by eliminating a protein it needs
to reproduce or cause infections.

20. Role in regulating gene translation
 Huntington’s disease
 Disease caused by toxin protein,
that affects more than 30,000
people.
 Gene silencing aims to reduce
the production of the mutant
protein by shut down the
expression of the gene coding
for the aberrant protein

21. Role in cancer pathogenesis
 miRNA are classified as:
1. Oncogenic: their increase expression lead to cancer
1. Tumor suppressor: their absence increase cancer
 Half of the identified miRNA (~300) are located at
chromosomal regions disrupted by rearrangement
in cancer pathogenesis

22. Oncogenic miRNA
(miR-17-92)
Tumor suppressor
miRNA (miR-15 & miR-16)
 Located in 13q31
 Expression of miR-17-92 increased in
small cell lung cancer
 It target RB2 and E2F1 responsible
for regulating cell cycle (tumor
suppressor genes)
 Located in 13q14
 Deletion of miR-15 & miR-16 will reduce
their expression  chronic lymphocytic
leukemia (CLL)
 miR15+16 BCL2apoptosis
 Deletion of miR15+16
BCL2apoptosis
Role in cancer pathogenesis

23. CONCLUSION

24. Conclusion
 Eukaryotes use dsRNA as an agent of gene silencing, in a process called RNAi
 Special enzymes (Drosha and, most generally Dicer) recognize dsRNA and generate
from that short (21-22 nucleotide) RNAs that are the active species for gene
silencing.
 The dsRNAs that give rise to siRNAs can arise from various sources ranging from
infecting viruses.
 siRNAs and miRNAs act in essentially the same way. They are incorporated into a
machine called RISC.
 miRNAs have also been associated with cancer, with some miRNAs being classified
as tumor suppressors and others as oncogenes.
 RNAi has become a regulator tool and is particularly useful in systems.

25. Thank You