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Cilia / flagella Flashcards

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1
Q

Are cilia and flagella the same structure?

A

Yes - used interchangeably. 1/2 tends to be flagella, many tends to be cilia.

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2
Q

Where are centrioles?

A

In the centre of the centrosome.

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3
Q

What is chlamydomonas?

A

Green algal model organism very similar to yeast. Helped us understand how cilia form.

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4
Q

What are motile cilia used for?

A

Body patterning.

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5
Q

What are non-motile cilia used for?

A

Sensing.

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6
Q

What are ciliopathies?

A

Diseases involving defective cilia.

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7
Q

What did Theodor Boveri (cell biology pioneer) say?

A

Centrosome (and centrioles within) is the true division organ of the cell.

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8
Q

What is the structure of centrioles?

A

Highly organised microtubule cylinders (9 triplets of MTs) (radially symmetric). There are 2 per centrosome, organised at right angles to each other.

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9
Q

How often do centrioles replicate?

A

Once per cell cycle. Cells must inherit 1 centriole (2 orthogonal MT cylinders).

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10
Q

What is the function of a centriole?

A

Forms the base of cilia / flagella.

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11
Q

How do we know the centrioles are not involved in cell division?

A
  • MT nucleation (making spindles / segregating chromosomes) is in the PCM.
  • Centriole destruction does not inhibit cell division.
  • Higher plants and some animals don’t have centrioles.
  • Drosophila don’t need centrioles to develop into a mature fly (KO experiment).
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12
Q

What problems did develop in the centrioleless Drosophila?

A

Severe issues where cilia function was required (sperm cells or sensory neurons).

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13
Q

Why do we think centrioles are present in centrosomes?

A

They are hitchiking on existing segregation machinery so that the centrioles are always present in both daughter cells.

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14
Q

What is the difference between cilia and flagella?

A
  • Number on a cell
  • Beat pattern
  • Frequency of beats
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15
Q

What are cilia / flagella?

A

MT extensions of the centriole.

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16
Q

What is the structure of cilia / flagella?

A

Highly organised microtubule cylinders (9 doublets of MTs) (radially symmetric). Also 2 central independent MTs. ‘9 + 2 MT organisation’. Continuations of 2/3 of the centriole MTs.

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17
Q

What beat pattern do flagella have?

A

Beating side to side like a fish swimming (faster).

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18
Q

What beat pattern do cilia have?

A

A stroking pattern (slower), in coordination with other cilia.

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19
Q

Where are motile 9 + 2 ciliated cells found?

A
  • Respiratory tract
  • Cerebrospinal fluid (cortex)
  • Female reproductive tract (fallopian tubes)
  • Sperm cells
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20
Q

What do cilia do?

A
  • Move fluid (or eggs)
  • Move cells within fluid
  • Sense
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21
Q

How do the cilia beat?

A

Dynein proteins connect the adjacent doublet MTs. They move the doublet along the neighbouring doublet, causing the cilia to bend. It bends until it can’t go further, then snaps back.

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22
Q

Where are motile 9 + 0 ciliated cells found?

A
  • Embryo (nodal cilia)
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23
Q

Where are non-motile 9 + 2 ciliated cells found?

A
  • Inner ear (kinocilium)
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24
Q

Where are non-motile 9 + 0 ciliated cells found? (SENSORY)

A
  • Kidney
  • Bile duct
  • Pancreas
  • Bone / cartilage
  • Eye (rod cells)
  • Nose (olfactory neurons)
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25
Q

What properties of chlamydomonas make it useful for study?

A
  • Simple genetics
  • Can KO genes
  • Has chloroplasts so photosynthesises
  • Has 2 cilia giving it motility
  • Has eyespot causing negative phototaxis
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26
Q

What have centrioles previously been known as?

A

Basal bodies (base of flagella).

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27
Q

What did study of chlamydomonas reveal about centrioles?

A
  • How they are built
  • How they are dynamic
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28
Q

Are cilia proteins synthesised in the cilia?

A

No (no ribosomes) - they are transported to it from a different site in the cell.

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29
Q

What is the size of cilia?

A

Very small.

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30
Q

How was it discovered that cilia are dynamic?

A

One chlamydomonas cilium was cut off - it grew back and the other one shrank to meet it. Then they both grew back together.

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31
Q

What is happening when the cilia are at a steady state?

A

Turnover - tubulin subunits being added and removed.

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32
Q

Where does growth of cilia occur?

A

Tips, not base.

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33
Q

How did we discover where cilial growth happens?

A

Fused a mutant chlamydomonas with short cilia to one with normal growth. Normal growth organism’s tubulin was epitope tagged. Therefore could observe tubulin being added to mutant cilia was at the tips.

34
Q

What happens to cilia when a cell divides?

A

They disassemble, centrioles divides with centrosomes, then they reassemble in the new cell.

35
Q

What happens to cilia when a cell is under stress?

A

They are lost.

36
Q

How are cilia assembled?

A

Intraflagellar transport (IFT).

37
Q

What is IFT?

A

Trains of IFT proteins travel to / from the cilium tip between the outer doublets of MTs and plasma membrane. Relies on kinesins and dyneins within the flagella.

38
Q

Can flagella be formed when kinesin used in IFT is mutated?

A

No. ie IFT required for flagella formation.

39
Q

How was IFT discovered?

A

DIC videomicroscopy of paralysed flagellum.

40
Q

How was cilia protein composition observed?

A

Sucrose density gradient profile.

41
Q

Why did we think IFT proteins are highly conserved?

A

They were found in seemingly unrelated groups of proteins (sensing in the worm and building cilia in the chlamydomonas).

42
Q

What do IFT protein complexes do?

A

Carry material and deposit it at the cilium tip.

43
Q

How are IFT proteins transported towards the tip?

A

Kinesin-II protein.

44
Q

What direction is towards the tip?

A

Anterograde.

45
Q

How are IFT proteins transported towards the base?

A

Cytoplasmic dynein 2.

46
Q

What direction is towards the base?

A

Retrograde.

47
Q

What happens when either IFT transport motor protein is mutated?

A

Flagellum formation (ciliogenesis) is prevented.

48
Q

Are IFT proteins conserved?

A

Yes - they are found in eukaryotes that have cilia / flagella. (Motors, IFTA and IFTB).

49
Q

What is ciliary gating?

A

Structures (‘transition fibres’) at the ciliary base that allow or prevent proteins from entering the cilia. Thought that molecules are tagged to be let into the cilia.

50
Q

What questions remain about cilia?

A
  • How does ciliary gating work?
  • How cargo is deposited / reloaded at the tip?
  • How do ciliary membranes form / change?
51
Q

What is Kartagener syndrome?

A

A syndrome caused by immotility in cilia.

52
Q

What are Kartagener syndrome symptoms?

A
  • Chronic sinusitis
  • Bronchiectasis
  • 50% situs inversus (flipped body pattern)
  • Infertility
53
Q

Why are cilia immotile in Kartagener?

A

Dynein molecules linking MT doublets in cilia are missing.

54
Q

Why does cilia immotility cause situs inversus?

A

Left-right asymmetry (differential gene expression) is developed early in mammalian development due to movement of cilia.

55
Q

What happens to break embryonic symmetry?

A

The embryonic node cells (sheet of epithelial cells) have 1 ‘9 + 0’ cilium each. They beat in a circle and cause extraembryonic fluid to have net flow past the embryonic node from right to left of the embryo.

56
Q

What beating pattern do embryonic node cells have?

A

Rotary / circular.

57
Q

How might the embryonic asymmetry develop?

A
  • Particles in extraembryonic fluid burst and deposit particles at one side of the node. The contents are detected by sensory cilia.
  • Flow itself causes cilia to bend which activates mechanosensitive ion channels and triggers gene expression.
58
Q

What do sensory cilia act like?

A

Antennae

59
Q

How is the cilium in rod cells different to epithelial cells?

A

It is large and more expanded (evolved).

60
Q

What are properties of the olfactory neuron (nose) cilia?

A
  • Found at the dendritic knob
  • Contain g-protein coupled odorant receptors
61
Q

What is a primary cilium?

A

A sensory cilium that forms in non-specialised cells when they are starved for growth factors (in conditions that don’t favour mitosis).

62
Q

Where have primary cilium been observed to form?

A
  • Retinal pigment epithelium (RPE) cells
  • Mouse skin fibroblasts
63
Q

What is polycystic kidney disease (PKD)?

A

A disease caused by lack of signals from primary cilia. Many cysts (uncontrolled cell division) develop on the kidneys. This blocks kidney tubules.

64
Q

What forms of PKD are there?

A
  • Autosomal dominant (common): mutations in sensory ion channels
  • Autosomal recessive: mutations in IFT proteins
65
Q

When does PKD develop?

A

Late onset; symptoms only get worse when you’re older.

66
Q

Why does PKD develop?

A

Flow in kidney cannot be detected, which means signals leading to cell division arrest are not sent. Therefore cells keep dividing.

67
Q

Why do cysts develop in recessive PKD?

A

Mutations in IFT proteins mean primary cilia don’t form. Therefore they cannot detect flow and signal for cell division to stop.

68
Q

Why do cysts develop in dominant PKD?

A

Mutations in sensory ion channels mean the signals from the cilia are not propagated resulting in no signal for cell cycle to stop.

69
Q

How did we prove cilia bending caused signalling?

A

Fluid passed over cilia. Calcium sensitive fluorescent indicator detected calcium flow into cells (through ion channels) as a result of cilia bending.

70
Q

When is Ci / Gli an activator of transcription?

A

It has its C terminus - cleavage blocked by Smo ie Hh is present. (See pathway on Lecture 6, slide 27).

71
Q

When is Ci / Gli a repressor of transcription?

A

When its C terminus is cleaved.

72
Q

Smoothened (Smo) activation / repression

A
  • Activated by Hh
  • Repressed by Ptc
  • Activates Ci / Gli
73
Q

Hedgehog activation / repression:

A
  • Represses Ptc
74
Q

Patched (Ptc) activation / repression:

A
  • Repressed by Hh
  • Represses Smo
75
Q

How do mutations in IFT proteins impact neural tube development?

A

Same impact as Shh KO - neural tube is dorsalised.

76
Q

Is the Shh pathway active in cilia?

A

Yes.

77
Q

What happens when Shh is activated in the cilium?

A

Shh binds to Ptc causing Ptc to exit the cilium, and Smo to enter. Cleavage of Gli is blocked so it becomes an activator. Gli (either form) is exported from the cilium.

78
Q

How do cilia form?

A
  • Centrioles get close to plasma membrane
  • They start to grow doublet MTs.
  • Pushes plasma membrane upwards.
    OR
  • Cilia form internally
  • Membrane from
    (distorted) endomembrane vesicle
79
Q

What might different cilia formation mechanisms confer?

A

Different cilia functions.

80
Q

What can chlamydomonas do to avoid being captured by single celled organisms that feed on them?

A

Shed their flagella (captured via their flagella).

Cell Biology (7 decks)

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