Post transcriptional Gene silencing (miRNA & siRNA)

1. siRNA and miRNA
Presented by:-
Vivek kumar
M.Sc 2nd Sem
microbiology
Bangalore university

3. Introduction
Gene silencing is a technique that aims to reduce or
eliminate the production of a protein from its
corresponding genes.
It is generally describe the “switching off” of a gene
by a mechanism other than genetic modification.
It occurs when RNA is unable to make a protein
during translation.
Gene silencing is same as gene knock down but is
totally different from gene knock out.

4. There are so many approches for gene
silencing
Gene Knockout.
Gene knockdown.
Gene silencing and degradation of gene using RNA
technology.
1. Antisense RNA technology.
2. RNAi technology.

5. Genes are regulated at either the transcriptional level or
post transcriptional level
Transcriptional gene silencing
 Genomic Imprinting.
 Praramutation.
 Transposon silencing.
 Transgene silencing.
 Position effect.
 RNA-directed DNA
methylation.
Post transcriptional gene silencing
 Antisense RNA technology.
 RNAi technology.
miRNA.
shRNA.
siRNA.

6. RNAi
• RNAi is a mechanism that inhibits gene
expression at the stage of translation or by
hindering the transcription of specific genes
thus stopping production of protein.
• It was 1st discovered in 1988 by Andrew fire
and Craig Mello in the nematode worm
C.elegans and later found in a wide variety of
organisms including mammals.

7. Need for RNA interference.
1. Defense mechanism:-
a) Defense against infection by viruses etc.
b) As a defense mechanism to protect against
transposons and other insertional elements
2. Genome wide Regulation:-
a) RNAi plays a role in regulating development and
genome maintenance.

8. In interference:-
1. RNAi :-
1. siRNA :- dsRNA 21-22nt.
2. miRNA:- ssRNA 19-25nt. Encoded by non- protein coding
genome.
2. RISC :-
1. RNA induced silencing complex, that cleaves mRNA.
3. ENZYMES:-
1. DICER:- Produces 20-21nt cleavages that initiate RNAi.
2. DROSHA:- Cleaves base hairpin in to form pre miRNA; Which
is later processed by Dicer.

11. miRNA
It is a non coding RNA molecule of approx 21-23 nt.
that inhibits the mRNA expression is known as
miRNA.
The formation of micro RNA (miRNA) consists of
three important steps:-
Formation of primary miRNA.
Formation of precursor miRNA.
Formation of mature functional miRNA.

13. siRNA
also as short interfering RNA or silencing RNA.
It is a class of double - stranded RNA molecules.
It is 20-25 bp in length.
It is similar to miRNA.
Operating withing the RNA interference RNAi
pathway by the enzyme Dicer.
It interferes with the expression of specific genes
with complementary nucleotide sequences by
degrading mRNA after transcription, resulting no
translation.

16. Significance of RNAi
RNAi protects against viral infection.
RNAi secures genome stability by keeping mobile
elements silent.
RNAi mechanisms repress protein synthesis and
regulate the development of organism.
RNAi offers a new experimental tool to repress gene
specifically.
RNAi might be a useful approach in future gene
therapy.

17. Applications
Testing hypothesis of gene function.
Target validation.
Pathway analysis.
Gene Redundancy.
Functional screening.
siRNA as therapeutics.

18. Reference
• Molecular Biology of the Gene , 5th edition by
Watson Baker Bell Gann Levine Losick ;
chapter-18 Pgno.- 567-570.

19. THANKYOU