DESCRIPTION OF USES OF CYTOSKELETON AND RELEVANT CLINICAL APPLICATION

1. The Cytoskeleton And Their
Applications In: Cancer, Cell Growth
And Congenital Diseases
Jesca Ghaston Bisigoro
Peter Nasuika Mshali
Evans A. Mlay
Neville Muhumuza
FACILITATOR: PROF. DAVID NGASSAPA

2. What would happen if someone snuck in during the night and stole your
skeleton? Just to be clear, that’s not very likely to happen, biologically
speaking. But if it did somehow happen, the loss of your skeleton would cause
your body to lose much of its structure. Your external shape would change,
some of your internal organs might start moving out of place, and you would
probably find it very difficult to walk, talk, or move.

3. Objectives
BY THE END OF THIS PRESENTATION YOU SHOULD BE ABLE TO:
• Define cytoskeleton
• Identify the three structures that make up the cytoskeleton
• Explain the general and specific functions of each of each of the cytoskeleton
structures
• Be able to explain each structures’ application in cell growth, cancer and
congenital anomalies

4. Outline
1. Definition of cytoskeleton
2. Microtubules
3. Microfilaments
4. Intermediate filaments

5. 1. DEFINITION
• A complex network of interlinking protein filaments and tubules in the cytoplasm.
• Responsible for maintaining cellular form and movement
• Extends throughout the cytoplasm from the nucleus to the plasma membrane.

6. ACTIN FILAMENT/MICROFILAMENT
INTERMEDIATE FILAMENT
MICROTUBULE
THERE ARE 3 MAJOR
TYPES

7. 3 types of cytoskeleton and locations in a cell

8. MICROTUBULE
3D reconstructed image of a microtubule

9. • “Micro” in their name should not confuse you.
• microtubules are the largest out of the 3.
• with an outer diameter of about 25 nm.
• made up of tubulin proteins arranged to form a hollow, straw-like tube
• each tubulin protein consists of two subunits, α-tubulin and β-tubulin.
wall thickness=5nm
Inner diameter
14nm
Outer diameter
24-25nm

10. MICROTUBULE FILAMENT

11. Properties
• Microtubules can grow very long and highly dynamic
• Ability to rapidly polymerize or depolymerize from the ends.
• The uniform orientation of the subunits results in a polar structure
• with one fast-growing plus-end of exposed β-subunits and one slow-growing minus-
end of exposed α-subunits.

12. • Polymerization of tubulin to form microtubules is
directed by a variety of structures collectively known
as microtubule-organizing centres.
• These structures include
1. Basal bodies : which anchors Flagella and cillia
2. Centrosomes (also MTOC): anchors spindle fibers

13. Image showing a CENTROSOME
Microtubule arrangement in Flagella and Cillia is a fused 9+2 arrangement

14. Microtubule roles
• Structural role providing shape and rigidity of the cell
• They aid in cellular processes : mitosis, cytokinesis, vesicular
transport . These roles are achieved through:
1. Cilia and flagella which project from the surface of cell and
are active in locomotion of the cells. Eg fallopian tube and
sperm
2. Basal bodies present at the base of each cilium or flagellum
3. Centriole :located at the mitotic spindle of cells used in cell
division, also organise cell skeletal system.

15. Centrosome is a cellular structure involved in the process of cell
division. Before cell division, the centrosome duplicates and then, as
division begins, the two centrosomes move to opposite ends of the
cell. Proteins called microtubules assemble into a spindle between
the two centrosomes and help separate the replicated chromosomes
into the daughter cells.

16. Role of microtubules in congenital anomalies
Kartagener syndrome (Primary Ciliary Dyskinesia)
• Kartagener’s syndrome (KS) is a rare autosomal recessive genetic disorder
which was first described by Siewert in 1904; however, Kartagener
recognized the clinical syndrome in 1933.
• The syndrome includes the clinical triad of chronic sinusitis, bronchiectasis,
and situs inversus
• In KS, the gene mutation at DNA11 and DNAH5 which codes for dynein 
impaired ciliary motility, which predisposes to recurrent sinopulmonary
infections, infertility, and errors with left–right body orientation

17. DNA11 and DNA H5
mutations affect dynein
arm responsible for
cilliary action

18. Pathophysiology
• Lack or dysfunction of dynein arms, radial spokes, and microtubules of cilia are
recognized structural and functional abnormalities of ciliary ultrastructures,
encoded by the mutated genes DNAI1 and DNAH5.
• These faulty genes cause the cilia to be the wrong size or shape or move in the
wrong way, making ciliary motility defective.

19. Diagnostic criteria for KS
• history of chronic bronchial infection and rhinitis from early childhood
• combined with one or more of following features:
– (a) situs inversus or dextrocardia in a patient or a sibling,
– (b) alive but immotile spermatozoa,
– (c) absent or impaired tracheobronchial clearance, and
– (d) cilia showing characteristic ultrastructural defect on electron microscopy

20. Investigations
• High-speed video microscopy for assessing ciliary beat frequency and pattern,
transmission electron microscopic for detecting ultrastructural ciliary defect,
• genetic test for DNA11 and DNAH5 mutations are confirmatory laboratory
tests.
• Chest X-ray
• Sinus CT (PNS- para nasal sinus)

21. • Posteroanterior chest X-ray showing dextrocardia with right-sided aortic arch.
There is paracardiac and left lower lung bronchiectasis with fibrotic bands

22. Other findings
• reduced nasal nitric oxide level (~10% of normal)
• prolonged saccharin clearance time (>1 hour)
• reduced ciliary beat frequency (<11 Hz/second)
• absent ciliary ultrastructure (dynein arms) using electron microspcopy
• mutated DNAI1 and DNAH5 genes

23. Treatment
• Chest physiotherapy
• Mucolytics
• Antibiotics
• Influenza and pneumococcal vaccination should be routinely
given

24. • Neuro-degenerative diseases : Alzheimer’s disease, Huntington’s disease
and Amyotrophic lateral sclerosis

25. Amyotrophic lateral sclerosis
• Most common degenerative disease of the motor neuron system. Unkown cause.
• Named for its underlying pathophysiology, with “amyotrophy” referring to the
atrophy of muscle fibers, which are denervated as their corresponding anterior horn
cells degenerate.
• “Lateral sclerosis” : changes seen in the lateral columns of the spinal cord as upper
motor neuron (UMN) axons in these areas degenerate and are replaced by fibrous
astrocytes (gliosis).
• A mutation to a microtubule protein, the tubulin isoform TUBA4A, is sufficient to
cause a familial and rare form of ALS

26. Role in cancer
• In cancer chemotherapy Taxanes (docetaxel, Paclitaxel) , vinblastine and
vincristine, epothilones stabilise microtubules leading to apoptosis.
• Because tumor cells proliferate rapidly, they are more affected by
antimitotic drugs than are normal cells.
• Increased alpha-tubulin 1b used as an indicator of poor prognosis and
resistance to chemotherapy in Hepato-Cellular Carcinoma.

27. Role in cell growth
• The form mitotic spindle which aids in migrating chromosomes
• They organize cellular components and split them in two
• Provide anchorage for chromosomes.
• They make up the centrosome which is the main organising centre for
microtubules.

28. Parkinsons disease:
Parkinson's disease is a neurological movement disorder. Common
symptoms include tremor, slowness of movement, stiff muscles,
unsteady walk and balance and coordination problems. There is no cure
for the disease. Most patients can maintain a good quality of life with
medications.

29. Pathophysiology
• Loss of nigral dopaminergic neurons which have long axons enriched
with microtubules.
• Depolymerization of Microtubules by Parkinsons Disease toxins like
rotenone disrupts vesicular transport.
• accumulation of vesicles in the cell body leads to increased cytosolic
concentration of dopamine due to leakage of the vesicles
• Elevated oxidative stress induced by dopamine oxidation may thus
trigger the selective death of Dopaminergic neurons.

30. Treatment
• Levodopa/Carbidopa
• Bromocritpine
• Psychosocial support

32. Microfilaments

33. Microfilaments/Actin
• Long filamentous structures and major cytoskeletal protein in most cells.
• Actin constitute about 15% total protein of non muscle cells.
• Actin is present in muscle as a thin (5–7 nm in diameter)
• Composed of two chains of globular subunits (G-actin) coiled around
each other to form a filamentous protein, F-actin (double stranded helix)

35. The cytosolic actin filament. Actin dimers are added to the plus (+) end and removed at the
minus (–) end, dynamically lengthening or shortening the filament, as required by the cell.
Regulated in presence of ATP/ADP and calcium ions

36. Actin Filaments
3 classes:
• α-actin of muscle
• β-actin and γ-actin of non-muscle cells.

37. • In non-muscle cells, only about half of their total actin is in the filamentous
form, because the monomeric G-actin form is bound by small proteins,
such as profilin and thymosin, which prevent their polymerization.
• Actin filaments in muscle cells are structurally stable, in non-muscle cells
they readily dissociate and reassemble.

38. Roles of Actin Filaments
• In skeletal muscle, they assume an array integrated with myosin filaments aid
in muscle contraction.
• In most cells, actin filaments form a thin sheath just beneath the
plasmalemma, called the cell cortex, which is useful in endocytosis, exocytosis,
and cell migratory activity.

39. • Actin filaments are intimately associated with several cytoplasmic
organelles, vesicles, and granules.
• The filaments are believed to play a role in moving and shifting
cytoplasmic components (cytoplasmic streaming).

41. • Actin filaments are associated with myosin and form a "purse-string" ring of
filaments whose constriction results in the cleavage of mitotic cells.
• In most cells, actin filaments are found scattered in what appears to be an
unorganized fashion within the cytoplasm
• They are part of Microvilli  increase surface area for absorption

42. Roles of Actin in cancer
• Actin has a major role in EMT (epithelial to mesenchymal transition) and vice versa
which is key in metastasis of cancer cells. Current research is targeting actin
filaments.
• Transportation of cancer cells

43. Role of Actin in cancer cont…
• TR100, is effective in vitro and in vivo in reducing tumor cell growth in
neuroblastoma and melanoma models.
• TR100 is cardio-protective unlike current anti-mitotic drugs like vinka
alkaloids.

44. Application of actin in congenital diseases.
Actin-accumulation myopathy:
– ACTA1 gene mutation alpha actin
– Affecting how actin binds ATP
– Attachment (binding) and release of the overlapping thick and thin filaments
allows them to move relative to each other so that the muscles can contract.
– Dysfunctional actin-ATP binding may result in abnormal thin filament formation
and impair muscle contraction

45. Symptoms of Actin accumulation myopathy
• Severe muscle weakness (myopathy)
• poor muscle tone (hypotonia) throughout the body.
• In infancy:
– they include feeding and swallowing difficulties
– weak cry
– difficulty with controlling head movements.
– "floppy" babies and may be unable to move on their own.

46. • The severe muscle weakness that occurs in actin-accumulation myopathy.
• Affects the muscles used for breathing.
• Individuals with this disorder may take shallow breaths (hypoventilate)
especially during sleep, resulting in a shortage of oxygen and a buildup of
carbon dioxide in the blood.
• Most children die in infancy.

47. Nemaline rod myopathy:
– Mutations in ACTA-1, NEB genes etc  defective alpha-skeletal-
actin
– Muscle weakness and presence of thin fibres in muscles on
microscopy (nemaline rods )
– muscle weakness, hypotonia and reduced or absent reflexes. most
severe in muscles of the face, neck and proximal muscles.
– Lethal and few infants make it to their first birthday.

48. Application in cell growth
• A contractile ring of actin and myosin-II is used to pinch off daughter
cells during cytokinesis
• Neurons destined to control the intestine migrate large distances as
neural crest cells during development with the aid of actin filaments.

49. Image showing role of actin in cytokinesis

50. Intermediate Filaments (IF)

51. Intermediate Filaments
• Intermediate filament (IF) supergene family are ubiquitous(every
where in the cell) structural components.
• Distributed in both the cytoplasm and the nucleus.
• 5 cytoplasmic IF groups and 6th Type comprised of Lamins reside in
the nucleus

52. Properties Of Intermediate Filaments
1. Diverse primary structure
2. Non-polar architecture
3. Relatively insoluble
4. High stability and mechanical strength
5. Distributed in cytoplasm and the nucleus

53. Structure of intermediate filament
• There are currently 70 genes encoding (IF) proteins.
• 10nm fiber with a Tripartite structure (split into 3 parts )
• Prototypical structure consisting of two polypeptide α-
helixes wound around each other
• The simplest soluble unit of IF proteins is a tetramer
consisting of two antiparallel dimers
• Ability to assemble into homo or polymeric filaments

54. Image A of intermediate filaments showing its tripartite structure
“Tripartite” means to split
into 3
The schematic diagram B shows an intermediate filament protein dimer
B
A

55. 1. Image A: showing molecular arrangement of Ifs
2. Image B: showing electron microscope image of Ifs in a cell.
A
B

57. Roles of IF
• Provide structural support for the cell and anchorage.
• Form a deformable three-dimensional structural framework for the cell
• Provide an adaptable connection between the cell membrane and the cytoskeleton
• Furnish a structural framework for the maintenance of the nuclear envelope as well
as its reorganization subsequent to mitosis

58. Role of IFs Cont…
• Providing physical support and stability to cells and tissues resisting mechanical
stress and tension
• Provide internal scaffolding attachments to desmosome and hemidesmosome
complexes (cell-cell attachment)
• Initiate signaling cascades when interacts with other proteins eg. Vimentin regulates
VAV2

59. Image showing intermediate filament arrangement in cells

60. Role In Cancer
• Depletion or mutation of keratin often increases migration rates of cancer
cells which is likely to contribute to metastasis.
• keratin’s expression pattern has been utilized as a diagnostic tool for many
epithelial cancers. Because epithelial cells maintain the pattern of their
origins. Hence is used as a marker. Eg Keratin 17 in basal cell cancer, breast
cancer and Ca.Cervix. Imagine a son that maintains his father’s name.

61. • Vimentin is highly expressed in normal mesenchymal
cells whilst being absent in epithelial cells. Vimentin
expression has been increased in many cancers with
poor prognosis. Eg basal cell cancers.
• A cancer Tumor inhibitor Withaferin A (WFA) binds
vimentin causing it to aggregate  apoptosis of
tumour cells like Ca Breast, osteosarcoma.,
melanoma.

63. Role in cell growth
• Interactions between cytoplasmic IFs and other cellular proteins
initiate signaling cascades that regulate responses to processes
such as growth, migration, and apoptosis—all cellular processes
fundamental to development and embryogenesis.

64. Role in cell growth
• Vimentin plays a role in promoting stemness of mammary epithelial cells which
provide the basis for mammary gland growth.
• Provides cell stability after mitosis.
• But also for cell differentiation during development of the placenta, which has been
shown to involve differential expression of keratins

65. Congenital illnesses related to IFs
Epidermolysis bullosa simplex
• mutations in the genes encoding
keratins 5 and 14
• associated with blistering in the
epidermal basal-cell compartment
(where keratins 5 and 14 are the
major keratins) after mild frictional
trauma, such as rubbing of the skin.

66. MYOPATHIES AND LENS DISORDERS
Desmin myopathy
• Gain-of-function mutations in αB-crystallin
also cause desmin-related myopathy,
whereas loss-of-function mutations cause
congenital cataract
• Typically, the illness presents with lower
limb muscle weakness slowly spreading to
involve truncal, neck-flexor, facial, bulbar
and respiratory muscles.

67. Hutchison Gilford Progeria (HGPS)
• Mutation In Lamini A gene. Chance
mutation. 1 in 20 million.
• Rare fatal. Chance is 1 in 4-8 million
• Cause of aging unknown.
• Characterized by Premature ageing
• Stiff knee, “pear shaped chest”
prominent abdomen
• Micrognathia (small jaw for head)
• Osteolysis.
• “horse-riding stance”
• Heart failure , arteriosclerosis

68. Charcot Marie Tooth
An inherited nerve problem.
• Neurofilaments (NFs) are the
major intermediate filaments (IFs)
of mature neurons. Mutations
gained.
• It causes abnormalities in the
peripheral nerves that supply feet,
legs, hands, and arms. It affects both
motor and sensory nerves.

73. REFERENCES
• https://www.khanacademy.org/science/biology/structure-of-a-cell/tour-of-organelles/a/the-cytoskeleton
• Sanghvi-Shah et al Intermediate Filaments at the Junction of Mechanotransduction, Migration, and
Development ; Frontiers in Cell and Developmental Biology Vol.5 2017
https://www.frontiersin.org/article/10.3389/fcell.2017.00081
• https://www.mdpi.com/journal/ijms/special_issues/intermediate_filaments
• https://www.nejm.org/doi/full/10.1056/nejmra040319
• https://pubmed.ncbi.nlm.nih.gov/27803112/
• https://pubmed.ncbi.nlm.nih.gov/25621895/
• https://biomedicine.imedpub.com/cytoskeletal-molecules-play-a-major-role-in-cancer-progression.pdf
• Intermediate Filaments ; Human Protein Atlas 2021.
• https://www.proteinatlas.org/humanproteome/cell/intermediate+filaments
• C.A Mutch et al (July 2015) Disorders of Microtubule Function in Neurons: Imaging Correlates Original
Research Pediatrics

74. THANK
YOU