MicroRNA and thier role in gene regulation

1. microRNA and
their role in gene
regulation

2. Introduction;
 Definition;
“ micro RNA is a small non-coding RNA molecule
that function in RNA silencing and post transcriptional
regulation of gene expression.”

3. History;
 First miRNA was discovered in 1993 by a group led by
Ambros .
 Its mode of action publication was published by
Ruvkun’s team.
 In 2000 and 2nd small RNA was characterize.
 The first human diseases associated with deregulation
of miRNA was chronic lymphocytic leukemia.

4. Location:
 On the basis of organism;
1. plants.
2. animal.
3. some virus.
 On the basis of cell;
1. Majority miRNA within the cell.
2. Some are extracellular.

5. Terminology:
 DGCR 8: (DeGeoge syndrome Critical Region):
“microproceser complex sub unit is a protein that
in human encoded by the DGCR 8 gene, but in other
organism like Drosophilla melanogester such protein is
called Pasha.
 Drosha: is a class 2 ribonuclease 111 enzyme that in
human encoded by the drosha gene.

6. Conti…
 Exportin 5: transporter protein that transport precurser
miRNA from nucluce to cytoplasm.
 Dicer: dicer is also known as endoribonuclease Diser or
helicase , is enzyme that in human is encoded by Dicer
gene. Dicer cleave double stand miRNA and pre-miRNa
in to short double stranded RNA.

7. Conti..
 AGO2 protein: ( stand for Argonaute)
this protein family play a central role in RNA silencing
process, as essential component of the Risc(RNA
inducer silencing complex).
 RISC: is a multi protein complex which incorporate one
stand of a single stranded RNA(ssRNA) fragment, such as
miRNA . The single strand act as a templet for RISK to
recognize complementary mRNA transcript and through
Argonute, it cleave the mRNA and this phenomena is
called RNA interference.

8. Biogenesis and function:
 Biogenesis of mircoRNA:
this process is carry out in two places
of the cell;
1. Nucleus:
 Transcription
 Nuclear processing
 Nuclear export.
2. Cytoplasm:

9. Nucleus:
1. Transcription:
 miRNA usually transcribe by polymerase 11 enzyme.
 Poly 11 attached with the promoter region of the DNA
sequence and transcribe the DNA.
 The resulting transcript is capped with specially
modified nucleotide at the 5’ end and spliced.

10. Nuclear processing:
1. Formation of hairpin loop structure.
 Hairpin is composed of 70 NT each.
 This hairpin is recognized through type of protein called
GDCR 8.
 GDCR 8 associated with Drosha that cut DNA making
micro processing complex.
 This complex convert the pri-miRNA to pre-miRNA.
 Pre-miRNA that are spliced is known as "Mirtrons”.

11. Nuclear export:
 Pre-miRNA transport through a nucleocytoplasmic
transporter protein known as Exportin-5.
 Use GTP as energy.

12. Cytoplasmic processing:
 the pre-miRNA hairpin is cleaved by the RNase III
enzyme Dicer.
 Dicer interact with the 5’ and 3’ hairpin and cut the
loop.(means shorting the dsmiRNA).
 AGO2 bind with the dsmiRNA and unwinded and convert
to single stranded guide miRNA.
 Guide strand is complementary to the target mRNA and
inactivate the mRNA trough two process.
1. Cut on mRNA .
2. Inhibition.

13. RNA induce silencing
complex(RISC).
 Also known as microRNA ribonucleoprotein complex.
 Mature miRNA incorporate with RISC, which contain
Dicer and many other associated proteins.
 Argonaute protein(endonuclease) in RISC induce
silencing, which contain two domains one for binding
miRNA at 3’ end and other for binding with 5’ end of
miRNA.
 Argonautes cleave target transcripts directly and
sometime recruit additional proteins to achieve
translational repression. And this depend on the
complementarity of miRNA with mRNA.

14. Mode of silencing.
 Silencing may occur either through
degradation or preventing mRNA from
being translated.
 The relation of miRNA and its target is
base on negative regulation of target
mRNA.
 Here common scenario is use i-e feed-
forward loop.

15. Cellular Functions of miRNA
MicroRNA role in
translation process.
 Repression
mechanism on the
initiation complex or
recruiting 40S
ribosomal
subunit(M1).
 Repression
mechanism on
ribosome
assembly(M2).
 Repression
mechanism on
translation
process(M3).
 Degradation of
mRNA(M7,M8)

16. Nine Mechanism Of miRNA In
Gene Regulation.
1. 40S initiation inhibition.
2. 60S ribosomal unit joining inhibition.
3. Elongation inhibition.
4. Ribosome drop-off(premature
termination).
5. Co-translational nascent protein
degradation.
6. Sequestration in P-bodies.

17. Continue………
7. mRNA decaying(destabilization)
8. mRNA cleavage.
9. Transcriptional inhibition through miRNA-
mediated chromatin reorganization
followed by gene silencing.