Nucleus and Subnuclear structure

Question 1

How are HeLa cells stained?

Answer 1

Red for NPC. Green for nucleolus and blue for chromatin.

Question 2

What is the nuclear envelope?

Answer 2

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.

Question 3

What is the nuclear lamina?

Answer 3

Dense fibrillar network inside the nucleus which is composed of intermediate filaments and membrane associated proteins/

Question 4

What support does the nuclear lamina provide?

Answer 4

Mechanical support but also regulation of cellular events and chromatic organisation.

Question 5

What are laminopathies?

Answer 5

Group of rare genetic disorders caused by mutations in genes encoding proteins of the nuclear lamina/

Question 6

What are the main clinical symptoms of laminopathies?

Answer 6

Varying, including skeletal and or cardiac muscular dystrophy, lipodystrophy and progeria.

Question 7

What are the main mutations of laminopathies?

Answer 7

Lamin A/C and nuclear lamina associated proteins like emerin.

Question 8

Are there cures for laminopathies?

Answer 8

No only symptomatic treatment.

Question 9

Emery Dreifuss muscular dystrophy

Answer 9

Affects skeletal and cardiac muscle
Contractures
Progressive muscle weakness and atrophy

Question 10

Hutchison Gilford progeria syndrome (HGPS)

Answer 10

Progeria
Point mutation in LMNA gene, lamin A lacks 50 a.a.

Question 11

Euchrochromatin

Answer 11

DNA is active

Question 12

Constitutive heterochromatin has DNA that is…

Answer 12

Never expressed

Question 13

Faculative heterochromatin has DNA…

Answer 13

Differentially expresssed DNA

Question 14

NPC

Answer 14

Nuclear pore complex

Question 15

What is NPC structure?

Answer 15

Octagonally organised symmetric cylinder, embedded in two nuclear membranes.

Question 16

How do proteins get into the nucleus?

Answer 16

1. Protein with a nuclear localization signal
   sequence (NLS) is recognized by an importin
   complexed with GTP-binding protein, Ran (GDP)
2. Importin then binds cytoplasmic filaments
3. The complex is translocated through the pore
   by sequential binding to pore proteins
4. Nuclear guanine nucleotide exchange factor
   (GEF) exchanges the GDP on Ran for GTP,
   allowing protein to be released
5. Importin-Ran/GTP complex is re-exported,
   then cyoplamic GTP-ase activating protein (GAP)
   hydrolyses Ran to Ran-GDP, ready to go again

Question 17

How do proteins leave the nucleus?

Answer 17

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.

Question 18

Nup214

Answer 18

facilitates export of NES bearing cargo
- mutation can lead to accumulation of proteins in nucleus

Question 19

Triple A syndrome

Answer 19

Mutations associated with lack of accumulation of ALADIN into NPC.

Question 20

Triple A syndrome symptoms

Answer 20

Muscle control of heart and of oesophagus / sphincter
Adrenal insufficiency (affect hormone release)
Intellectual disability

Question 21

How does bulk mRNA exit nucleus?

Answer 21

Recruitment of multiple protein complexes on the mRNA make it stable and
export competent

Question 22

What mutation caused high grade tumours?

Answer 22

hTREX which is responsible for stability of mRNA and efficient nuclear export.

Question 23

3 major components of nucleolus?

Answer 23

fibrillar centers (FC)
dense fibrillar
components (DFC)
granular components (GC)

Question 24

Fibrillar centre (fc)

Answer 24

Depot of rDNA genes

Question 25

Dense fibrillar component (dfc)

Answer 25

Maturation of pre-mRNA transcripts

Question 26

Granular component (gc

Answer 26

Assembly of pre-ribosomal particles

Question 27

What are nucleoli formed around?

Answer 27

Nucleoli are formed around specific genetic loci called nucleolar organizing regions (NORs), comprise tandem repeats of rRNA genes

Question 28

Ribosomopathies

Answer 28

Ribosomopathies: a range of disorders in which genetic abnormalities cause impaired ribosome biogenesis/function, resulting in specific clinical phenotypes

Question 29

What is the nucleolus a biomarker of?

Answer 29

High grade tumours

Question 30

Nucleolus and virus infection

Answer 30

Redistribute cellular proteins into or out of the nucleolus either to : 1. Utilise nucleolar proteins to enhance virus replication 2. Subvert anti-viral pathways

Question 31

What virus localises to the nucleolus (example)

Answer 31

Coronavirus protein localised to the nucleolus

Question 32

What is targeted during herpesvirus infection?

Answer 32

Multiple proteins target the nucleolus.

Question 33

Sub nuclear structure examples

Answer 33

Nuclear speckles, cajal bodies, gemes. PcG bodies and PML bodies

Question 34

Number of nuclear sub-structures involved in splicing

Answer 34

Cajal bodies, gems and nuclear speckles

Question 35

Cajal bodies

Answer 35

Spherical sub organelles contain proteins that participitate biogenesis of mRNA.

Question 36

Nuclear gems

Answer 36

Do not contain small snRNPs but contain a SMN protein which functions in snRNP biogenesis.

Question 37

Spinal Muscular Atrophy

Answer 37

Incurable disease caused by a genetic defect in the SMN1 gene which codes SMN, a major Cajal body and Gem protein

Question 38

Nuclear speckles

Answer 38

Structures enriches in pre-mRNA splicing factors. Storage and modifications compartments for pre-mRNA splicing factors.

Question 39

Retinitis pigmentosa

Answer 39

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

Question 40

Polycomb bodies

Answer 40

Polycomb bodies are hubs for gene repression, usually associated with heterochromatin.

Question 41

PML bodies

Answer 41

Implicated in the regulation of diverse cellular functions

Question 42

Acute promyelocytic leukaemia

Answer 42

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

Question 43

Role of PML bodies

Answer 43

1. nuclear storage for the accumulation of proteins and release them when necessary 2. 'catalytic surfaces' where proteins accumulate to be post-translationally modified 3. active sites for specific nuclear functions such as transcriptional and chromatin regulation

Question 44

What do PML bodies regulate?

Answer 44

p53-dependent apoptopic and cellular sensescnece.

Question 45

PML bodies and virus infection

Answer 45

Part of interferon infuced host innate immune defence.