3. Flow of seminar
Introduction
Nuclear pore complex
Structure of nuclear pore complex
Mechanism of import and export of protiens
Rangtpase cycle
Rna transport
Research evidences
conclusion
4. What is NucleoCytoplasmic Transport ?
• Transport of thousands of macromolecules between
cytoplasm and nucleus occurs through nuclear pore
complex (NPC).
• Nucleocytoplasmic transport is regulated by complex
interplay of nuclear transport machinery which includes
elegant structure like nuclear pore complex ,nuclear
envelope protiens and transport receptors.
5. Why NC transportation is needed ?
• Nuclear envelope separates nucleoplasm from cytoplasm and controls
the nucleocytoplamic transport which is critical for many physiological
and pathological cellular process including gene expression,signal
transduction and oncogenesis.
• RNA transcripts are exported from the nucleus to reach the ribosomes
in the cytoplasm. Proteins such as histones, polymerases, transcription
factors, are imported into nucleus to reach the genetic material.
• Site of DNA replication and RNA biogenesis takes place in the nucleus.
• Site of Protein synthesis is cytoplasm.
6. NUCLEAR ENVELOPE
• Nuclear membrane is a physical barrier b/w nucleoplasm and cytoplasm.It
is a phospholipid bilayer which consists of inner and outer membrane and
are separated by perinuclear space.
• Outer membrane is in continuity with rough endoplasmic reticulum
studded with ribosomes which are engaged in protien synthesis.
• Nuclear membrane is perforated by NPC which fuse the outer nuclear
membrane and inner nuclear membrane together and creates a channel
for nucleocytoplasmic transport.
7. Nuclear Pore Complex
NPC is a multiprotein complex that serve as key regulator of molecular
trafficking b/w cytoplasm and nucleus.
10. CHARACTERISTICS OF NUCLEOCYTOPLASMIC
TRANSPORT
Selectivity:
RNA doesn’t goes through unless accompanied by specific protiens that
act as carriers ,DNA doesnt go through it.
Regulation Of Signals :
Protiens going into the nucleus must have a nuclear localization signal (
NLS) usually a sequence of 4 or more closely located positively charged
amino acids.
Protiens going out of nucleus must have a nuclear export sequence usually
a series of leucine with characteristic spacing b/w them.
12. Mechanism of import and export
Importin + Cargo ( In cytoplasm )→
releases in nucleus on binding with
RanGT
Exportin + Cargo + RanGTP (In
nucleus) → releases on conversion of
RanGTP into RanGDP
Atlanta cook et al
13. IMPORT AND EXPORT OF CARGO
Http7:Annual review in biochemistry/import and export of cargo
14. Ran gtpase cycle
• Ran exists in two conformations depending upon binding of GTP and GDP
• Ran GTPase is very high concentration in the nucleus whereas RanGDP is
very high concentration in cytoplasm.
• Conversion between GTP and GDP is triggered by two Ran specific
regulatory protiens that includes a cytosolic gtpase activating protien GAP
and a nuclear guanine exchange factor GAF.
16. How Directionality Achieved ?
• RanGDP / RanGTP Con.
Gradient
• RanGTP gradient is
maintained by asymmetric
distribution of GAP & GEF
• RanGTP stabilizes export
complex
• RanGDP stabilizes import
complex
SARA NAKIELNY et al
17. Transport Receptor – NTF2
• FG-Nup binding to NTF2
at the spot where Ran
binds upon import
• NTF2 vital for proper
balance of components
across Nuclear envelope
• Nuclear import of
RanGDP is mediated by
NTF2.
• NTF2 spec. recognized by
RanGDP
TIMOTHY et al
18. RNA TRANSPORT
The RNA molecules undergo a variety of post transcriptional processing
events, after which they are transported to their sites of function
throughout the cell.
the subcellular locations of each type of RNA namely messenger RNA
(mRNA), small nuclear RNA (snRNA), ribosomal RNA (rRNA), and transfer
RNA (tRNA) are critical to the normal functioning of the cell.
majority of RNAs are transported to the cytoplasm. Some RNAs need to be
reimported to the nucleus for their function.
All cellular RNA species exit the nucleus through NPCs by an active,
mediated mechanism
19. TRANSPORT OF mRNA
Processing events that influence Nuclear Export
Transcribed pre-mRNAs undergo three co/post transcriptional processing
events.
1. 5’ capping
2. Splicing
3. polyadenylation
20. MECHANISM OF m RNA TRANSPORT
• Trancribed in the nucleus by DNA polymerase II
• Majority of m RNA export is independent of Ran & karyopherin β family.
• The (TAP:p15) m RNA export factor is a heterodimer which helps in Mrna
transport.
21. TRANSPORT OF tRNA
• Transcribed in the nucleus by RNA polymerase Ш.
• t RNA molecules have to be processed before transport into th cytoplam.
• Further modification of tRNA occurs in the cytoplasm.
• Processing comprises
1. Excision of 5’ & 3’ terminal sequences.
2. Addition of CCA to the 3’ end.
3. Base modification.
4. Removal of introns and base editing.
22. RIBOSOMAL RNA TRANSPORT
• Transcribed in the nucleus by RNA polymerase I
• Nuclear export occurs in context to Ribosomal-subunits
• Transport requires energy & through NPC
23. THEMES & PERSPECTIVES
• Common theme :
transport in both
direction across
the NPC mediated
by RNA-binding
proteins
24. FUTURE ISSUES
• In order to determine the general principles of Ran-dependent transport,
the structure of each karyopherin bound cargoes is required.This will
reveal the mechanisms by which nuclear import/export signals,
particularly of cargoes such as NESs and NLS are recognized.
• In some of the cases, the same β-karyopherin can mediate both import
and export so there is need to know extensive studies on karyopherin.
• mRNA export pathway which is one of the complex process and different
mRNAs are recognized for export, process through which it is released to
the cytoplasm hence the nuclear transport machinery performs is need to
be known clearly.
25. Nuclear RNA Export and Its Importance
in Abiotic Stress Responses of Plants
V. Chinnusamy , Z. Gong , and J.-K. Zhu
The transduction of abiotic stresses to switch on genes involved in adaptive responses
are critical to the survival and reproduction of plants exposed to adverse environments.
Plants have evolved multiple stress response pathways, some of which are specific, but
others may be common for various abiotic stresses
Nucleocytoplasmic trafficking—entry of developmental/environmental signals
for gene expression and export of expressed gene products from the nucleus
through nuclear pores—plays a fundamental role in gene expression in eukaryotic
organisms.
26.
27.
28.
29. Role of mRNA Export in Abiotic Stress Response of Plants
• Dead box proteins (DBPs) with RNA helicase activity are involved in RNA metabolism
such as transcription, RNA processing, RNA decay, and nucleocytoplasmic transport. In
yeast and vertebrates, Dbp5 plays a crucial role in export competent Mrnp formation
in nucleus, transport of mRNP through the NPC, and release of mRNA from mRNP in
the cytosol. The role of DBP in mRNA export and abiotic stress response of flowering
plants came from the analysis of the mutant los4 (low expression of osmotically
responsive genes 4) of Arabidopsis .
(GONG et al)
• Role of nups in abiotic stres reaponae was demonstrated ATPNUP 160 mutant which
was hypersensitive to chilling stress .Map based cloning of ATNUP 160 revealed it to
NUP homologus to mammal NUP 160 ATNUP 160 flower show early flowering ATNUP
160 is critical for mrna export , cold resposnive genes expression ,cold tolerance as
well as plant development at normal temperatures
( Dong et al 2006 . Perry et al )
30. SAD 2 domain enhanced gene expression and stress response genes under
cold ABA hypersensitivity in seed germination and seedling growth , SAD 2 is
localized in the nucleus thus result suggested that sad 2 play a crucial role in
nuclear regulator of cold .
(versules et al .2006)
The cold-sensitive phenotype of los4–1 showed inhibited mRNA export
under cold stress conditions. In contrast, the cold-tolerant but heat-sensitive
los4-2 showed normal mRNA export under cold stress but was defective in
mRNA export from the nucleus at warm temperatures (Gong et al. 2005). The
results from los4 mutants demonstrated that LOS4 DEAD-box RNA helicase
plays an important role in mRNA export, which is necessary for abiotic stress
response.
(Gong et al. 2005).
31. CONCLUSION
NUCLEOPHORIN (NUP107–160 complex) proteins shown that they participate
in mRNA export and regulate germination,flowering,hormone response,host-
plant symbiotic interaction, and biotic and abiotic stress tolerance. Further
studies on various components of the nuclear mRNA export machinery in
plants and their role in abiotic stress response will be necessary to better
understanding the link between mRNA export and abiotic stress-responsive
gene expression.
32.
33. EgRBP42 from oil palm enhances adaptation to stress in
Arabidopsis through regulation of nucleocytoplasmic transport of
stress-responsive mRNAs
Wan-Chin Yeap1*, Parameswari Namasivayam2, Tony Eng Keong Ooi1, David Ross Appleton1,
Harikrishna Kulaveerasingam3 and Chai-Ling Ho2, 4*
( Sime Darby Plantation Berhad, Research and Development, Biotechnology and Breeding, Sime
Darby Technology Centre Sdn. Bhd., Serdang, Selangor Darul Ehsan, 43400 Malaysia)
OBJECTIVE - , an hnRNP-like RNA-binding protein from oil palm, which
could be necessary for rapid protein translation to confer abiotic stress
tolerance in plants.
34. MATERIALS AND METHODS
• Six-month-old oil palm seedlings (Dura) were used for abiotic stress
treatments and gene expression analysis.
• Wildtype Arabidopsis, transgenic lines of WT:Pro35SEgRBP42 and mutant
atuba2c were grown under controlled environment conditions at 22 °C, 65
% relative humidity and 120 μmolm-2 s-1 illumination under long day
conditions, 16 h of light followed by 8 h of darkness.
• Pro35S:EgRBP42 in pEG100 and pEG100 (wildtype) were coated on the
surface of gold particles and bombarded into leaf tissue sections, Biolistic
Particle Delivery System bombardments were conducted .
• Total RNA was extracted from oil palm leaves, Arabidopsis leaves and
Arabidopsis flower using NucleoSpin RNA plant (Macherey-Nagel, Düren,
Germany)and observed target gene expression between wildtype .
35.
36. Overexpression of EgRBP42 confers abiotic stress tolerance and accelerates
recovery in vegetative development
45. CONCLUSION
The overexpression of EgRBP42 in Arabidopsis confers
drought, cold, salinity and flood tolerance with enhanced
post-stress recovery. Through this we can propose a model
describing post-transcriptional nucleocytoplasmic transport of
stress-responsive mRNAs in response to different abiotic
stresses, leading to a better adaptation to environmental
changes
Editor's Notes
By contrast to other nuclear envelope proteins, NPC components are evolutionarily conserved between yeast, animals, and plants, indicating that these NPCs share a common progenitor
Individual transport rate of NPC are very high about 500 per sec in both the directions.
Mechanism of Import & Export
Importin binds with cargo in the cytoplasm and releases the cargo molecule in the nucleus on binding with RanGT and Exportin binds with cargo molecule and RanGTP in the nucleus which releases the cargo molecule on conversion of RanGTP into RanGDP. Transport receptors acts as chaperons which shuttle the cargo molecule through the nuclear pore complex. Few examples of transport receptors are Importinβ ,NTF-2 , etc. Ran is responsible for regulating the interaction of transport receptor & cargo. Nucleophorins with specific amino acid sequences involving phenylalanine & glycine is known as FG-Nups (hydrophobic binding site , forms filament & colonizes on both side of NP).
The direction of nucleocytoplsmic transportation of the cargo molecules depend on RanGDP / RanGTP concentration gradient. RanGTP gradient is maintained by asymmetric distribution of GTP activating protein(GAP) & GTP exchange factor (GEF). RanGTP stabilizes export complex and RanGDP stabilizes import complex
Continious movement of ran gtp from the nucleus depletes the nuclear levels of rangtp
Therefore Rangdp has to be reimported into the nucleus and catalyzed
The nuclear import of RanGDP is mediated by NTF2 NTF2 specifically recognizes Ran in its GDP-bound state
The continuous outflow of exportin-cargo complexes and
cargo-free importins from the nucleus would lead to depletion
of nuclear RanGTP and eventual shutdown of all
nuclear transport, thus necessitating that Ran be restored
to the nucleus. The return of Ran is mediated by another
transport factor, NTF2 [34, 35]. NTF2 is unrelated to the
importin b family, and it binds only RanGDP. Upon entering
the nucleus, NTF2 and RanGDP must dissociate
from each other, and Ran’s GDP must be replaced with
GTP. Both steps are fostered by a Ran-specific guanine
nucle
Most eukaryotic RNAs are produced in the nucleus by RNA polymerase I, II, or III.
Processing Events That Influence Nuclear Export: Most mRNAs are transcribed as pre-mRNAs, which generally undergo three posttranscriptional processing events: 50 capping, i.e. addition of a 7-monomethyl guanosine (m7G) cap structure to the 50 end of the transcript; removal of introns by splicing; and polyadenylation at a defined site within the 30 untranslated region
RIBOSOMAL RNA TRANSPORT: It is a common precursor that is completely processed and assembled into ribosomal subunits, all within the nucleolus Therefore, nuclear export of these rRNAs occurs in the context of ribosomal subunits. Beyond the fact that ribosomal subunit export is a unidirectional, saturable process that requires energy and All rRNAs except 5S rRNA are transcribed occurs through NPCs very little is known about export of ribosomes.
Relatively little information exists on the NUPs and NEFs required for mRNA export in plants
Bioinformatics analyses have identified several conserved NUPs from rice and Arabidopsis that are homologous to yeast and vertebrate NUPs (Neumann et al.2006). Since the nuclear mRNA export pathway is highly conserved across species (fungi, insects, vertebrate) and many proteins similar to NUPs and NEFs have been found in higher plants, the mRNA export process in higher plants appears to be similar to that of other eukaryotes.