Nucleus and Subnuclear structure Flashcards
How are HeLa cells stained?
Red for NPC. Green for nucleolus and blue for chromatin.
What is the nuclear envelope?
Double lipid bilayer. External membrane is continous with the RER and in internal membrane is where many inner nuclear membrane (INM) proteins are, mostly associated with the nuclear lamina.
What is the nuclear lamina?
Dense fibrillar network inside the nucleus which is composed of intermediate filaments and membrane associated proteins/
What support does the nuclear lamina provide?
Mechanical support but also regulation of cellular events and chromatic organisation.
What are laminopathies?
Group of rare genetic disorders caused by mutations in genes encoding proteins of the nuclear lamina/
What are the main clinical symptoms of laminopathies?
Varying, including skeletal and or cardiac muscular dystrophy, lipodystrophy and progeria.
What are the main mutations of laminopathies?
Lamin A/C and nuclear lamina associated proteins like emerin.
Are there cures for laminopathies?
No only symptomatic treatment.
Emery Dreifuss muscular dystrophy
Affects skeletal and cardiac muscle
Contractures
Progressive muscle weakness and atrophy
Hutchison Gilford progeria syndrome (HGPS)
Progeria
Point mutation in LMNA gene, lamin A lacks 50 a.a.
Euchrochromatin
DNA is active
Constitutive heterochromatin has DNA that is…
Never expressed
Faculative heterochromatin has DNA…
Differentially expresssed DNA
NPC
Nuclear pore complex
What is NPC structure?
Octagonally organised symmetric cylinder, embedded in two nuclear membranes.
How do proteins get into the nucleus?
- Protein with a nuclear localization signal
sequence (NLS) is recognized by an importin
complexed with GTP-binding protein, Ran (GDP) - Importin then binds cytoplasmic filaments
- The complex is translocated through the pore
by sequential binding to pore proteins - Nuclear guanine nucleotide exchange factor
(GEF) exchanges the GDP on Ran for GTP,
allowing protein to be released - Importin-Ran/GTP complex is re-exported,
then cyoplamic GTP-ase activating protein (GAP)
hydrolyses Ran to Ran-GDP, ready to go again
How do proteins leave the nucleus?
Proteins are targeted for export by specific amino acid sequences, called
nuclear export signals (NESs). LxxxLxxLxL, where “L” is often leucine.
NESs are recognised by exportins.
Nup214
facilitates export of NES bearing cargo
- mutation can lead to accumulation of proteins in nucleus
Triple A syndrome
Mutations associated with lack of accumulation of ALADIN into NPC.
Triple A syndrome symptoms
Muscle control of heart and of oesophagus / sphincter
Adrenal insufficiency (affect hormone release)
Intellectual disability
How does bulk mRNA exit nucleus?
Recruitment of multiple protein complexes on the mRNA make it stable and
export competent
What mutation caused high grade tumours?
hTREX which is responsible for stability of mRNA and efficient nuclear export.
3 major components of nucleolus?
fibrillar centers (FC)
dense fibrillar
components (DFC)
granular components (GC)
Fibrillar centre (fc)
Depot of rDNA genes
Dense fibrillar component (dfc)
Maturation of pre-mRNA transcripts
Granular component (gc
Assembly of pre-ribosomal particles
What are nucleoli formed around?
Nucleoli are formed around specific genetic loci called nucleolar organizing
regions (NORs), comprise tandem repeats of rRNA genes
Ribosomopathies
Ribosomopathies: a range of disorders in which genetic abnormalities cause
impaired ribosome biogenesis/function, resulting in specific clinical phenotypes
What is the nucleolus a biomarker of?
High grade tumours
Nucleolus and virus infection
Redistribute cellular proteins into or out of the nucleolus either to :
1. Utilise nucleolar proteins to enhance virus replication
2. Subvert anti-viral pathways
What virus localises to the nucleolus (example)
Coronavirus protein localised to the nucleolus
What is targeted during herpesvirus infection?
Multiple proteins target the nucleolus.
Sub nuclear structure examples
Nuclear speckles, cajal bodies, gemes. PcG bodies and PML bodies
Number of nuclear sub-structures
involved in splicing
Cajal bodies, gems and nuclear speckles
Cajal bodies
Spherical sub organelles contain proteins that participitate biogenesis of mRNA.
Nuclear gems
Do not contain small snRNPs but contain a SMN protein which functions in snRNP biogenesis.
Spinal Muscular Atrophy
Incurable disease caused by a genetic defect in the SMN1 gene which codes
SMN, a major Cajal body and Gem protein
Nuclear speckles
Structures enriches in pre-mRNA splicing factors. Storage and modifications compartments for pre-mRNA splicing factors.
Retinitis pigmentosa
Retinitis pigmentosa a genetic eye condition in which the vision progresses from night blindness to tunnel vision to complete blindness.
Retinal pigment epithelium (RPE) is the pigment cell sheet that feeds the retinal cells. The RPE is attached to an intricate system of blood vessels. Genetically linked to mutations in splicing factor, PRP31
Polycomb bodies
Polycomb bodies are hubs for gene repression, usually associated with heterochromatin.
PML bodies
Implicated in the regulation of diverse cellular functions
Acute promyelocytic leukaemia
A subtype of acute myeloid leukaemia – caused by mutations in PML protein
In APL, there is an abnormal
accumulation of immature
granulocytes which show
characteristic hypergranular
morphology. This results in loss
of granulocytes, neutrophils etc
In 95% of cases of APL, PML protein forms a reciprocal translocation with the
retinoic acid receptor-alpha (RARα) gene
Role of PML bodies
- nuclear storage for the accumulation of
proteins and release them when necessary - ‘catalytic surfaces’ where proteins accumulate
to be post-translationally modified - active sites for specific nuclear functions such
as transcriptional and chromatin regulation
What do PML bodies regulate?
p53-dependent apoptopic and cellular sensescnece.
PML bodies and virus infection
Part of interferon infuced host innate immune defence.
