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BMS247 - Stem cells > Regeneration > Flashcards

Regeneration Flashcards

1
Q

What are the differences between the lifespan of some of the cells in the body?

What are examples of these cells?

A

1) Some live as long as the organism (eg. neurons)
2) Some are constantly replaced from stem cell (eg. blood and epithelia)
3) Some are REFORMED after injury/tissue damage, they are quiescent until damage/injury (eg. skeletal muscle cells)

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2
Q

What is regeneration?

A

The possibility of the FULLY DEVELOPED organism to replace ORGANS or APPENDAGES by growth or repatterining of the EXISTING tissues

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3
Q

Does the complexity of the organism determine if an organism can regenerate?

A

NO

  • C.elegans are very simple but CANNOT regenerate
  • Some lower vertebrates are very good at regenerating
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4
Q

What organisms can regenerate an entire organism from a FRAGMENT their body?

A
  • Flatworms
  • Starfish
  • Hydra
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5
Q

What are the 2 types of regeneration that can occur?

A

1) MORPHOLLAXIS

2) EPIMORPHOSIS

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6
Q

What is morphollaxis?

A

Repatterining WITHOUT growth:

  • No changes to the cell number
  • Shift in the fates of the cells already existing –> regenerate positional values
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7
Q

What is epimorphosis?

A

Regeneration by GROWTH:

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8
Q

How does epimorphosis occur?

A

GROWTH ZONE formed at the position of the cut

Growth zone then causes proliferation and regrows the MISSING PARTS of the structure

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9
Q

What is the structure of the hydra?

A

2 germ layers (endoderm and ectoderm)

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10
Q

How does the hydra regenerate?

A

By MORPHALLAXIS:

- NO growth

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11
Q

How does the hydra grow?

A

Continuously, with cells constantly changing their positional values

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12
Q

How do cells change their positional values?

A

By changing their FATES

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13
Q

What are the 2 gradients in the hydra that allow regeneration?

A

1) Gradient in POSITIONAL VALUE
- From the head region (pos. 1 being near the head)

2) HEAD INHIBITOR gradient

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14
Q

What does the PV of cells in the hydra determine?

A

Both:

  • The head inducing ability (high at region 1)
  • Resistance to the head inhibitor
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15
Q

What does the head inhibitor gradient do?

A

Forms a gradient along the body to prevent extra heads from forming

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16
Q

What happens when transplant a piece of region 1 tissue into region 3 of the body of a host hydra?

Why?

A

NOTHING HAPPENS

  • Region 3 has high level os head inducer activity
  • But level of the head inhibitor is high enough to prevent head induction
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17
Q

What happens when transplant a piece of region 1 tissue into region 3 the body of a host hydra, when the HEAD of the HOST hydra is REMOVED?

Why?

A

Second head forms

No head inhibitor to prevent the formation of a second head

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18
Q

Where is head inhibitor released from in the hydra?

A

The head

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19
Q

What happens if transplant a piece of region 1 tissue into region 5 of the body of a host hydra?

Why?

A

Second head will form

Low levels of the head inhibitor

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20
Q

What happens if remove the head of the donor hydra and leave it for 6 hours before transplanting tissue from region 1 (from donor) into region 3 of the host?

Why?

What happens if do this with region 4 and transplant into 5? Why?

A

Head will form

Positional values of the donor hydra change when the head is removed - cells in region 1 become more ‘head like’ –> stronger levels of head inducing capacity

Levels of the head inhibitor in the host hydra cannot overcome the new levels of the head inducer in region 1

4 –> 5:

  • This DOESN’T happen
  • Positional values have not changed enough for this region to be able to make high enough levels of head inducer
  • Must wait 30 hours
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21
Q

What signals are important in forming a head organiser?

A

Wnt signalling

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22
Q

What happens with GSK3 inhibition?

What does this cause?

A

UP REGULATION of nuclear beta catenin and therefore activation of the Wnt pathway

Causes:
- Animals to have characteristics of head organiser all along the body column

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23
Q

How is GSK3 inhibited?

A

Using Lithium

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24
Q

What is a urodele?

A

A ‘tailed’ AMPHIBIAN

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25
Q

How does regeneration in the urodele occur?

A

EPIMORPHIC:

- Through cell divisions making the new tissues

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26
Q

What can a urodele regenerate?

A
  • Dorsal crest
  • Limbs
  • Retina
  • Lens
  • Jaw
  • Til
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27
Q

Where does lens regeneration in the urodele occur from?

Why is this unusual?
What does this show?

A

From the iris

Unusual because the iris (neuronal) is a different germ layer to the lens (epidermal)

Shows that cells need to TRANSDIFFERENTIATE

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28
Q

What happens if resect the limb of the urodele?

A

Right structures are regenerated APPROPRIATE to where the cut is made

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29
Q

Where do the cells come from that allow tissues to regenerate in epimorphic regeneration?

A

Cells de-differentiate to reform the missing structures

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30
Q

What MUST happen for regeneration to occur in the urodele?

What happens if this is prevented?

A

Migration of the epithelial cells over the wound to close the wound

If prevented - NO regeneration

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31
Q

Why is the generation of a limb in development and regeneration different?

A
  • 10-fold size difference

- If morphogen gradients in regeneration –> have to work over a 10x larger range

32
Q

What happens in regeneration of the urodele limb after the epithelium has covered the wound?

A

Cells below the epithelium DEDIFFERENTIATE and form a blastema

33
Q

What is a blastema?

A

A mass of cells capable of growth and regeneration into organs or body part

34
Q

What forms the blastema?

A
  • From the DERMIS
  • From the DE DIFFERENTIATING muscle and cartilage
  • Sometimes from the muscle
35
Q

How can muscle help to form the blastema?

A

Can REVERT from multinucleate –> mononucleate cells

36
Q

What is the regenerative process in the muscle driven by?

A

Thrombin
Msx
Rb

37
Q

What allows re-entry of the muscle cells into the cell cycle?

A

Phosphorylation of Rb

38
Q

Are the cells in the blastema truly differentiated - are they like stem cells?

How is this seen?

A

NO

  • Very LIMITED trans-differentiation between the different cell types in the blastema
  • Some cross over between dermis and cartilage but the others are true to their cell type

Blastema just provides limited dedifferentiation potential

Seen by labelling various tissues axolotol cells with GFP and transplanting them into the limb

39
Q

What are the rules of epimorphic regeneration?

A

1) Regeneration is always DISTAL to the wound and according to the POSITIONAL VALE at the site of the cut
2) Blastema that forms has a morphogenetic autonomy after transplant
3) Regeneration is dependant on INNERVATION unless the limb is without a nerve from early on in development

40
Q

What is the experiment that shows the blastema to have morphogenetic autonomy after it has formed?

A
  • 2 amputations in the same organism (one at the upper arm and one at the hand)
  • Remove the cells from the tip of the cut at the upper limb and TRANSPLANT the blastema formed at the cut of the hand
  • Cells of the blastema will ONLY form the HAND (blastema autonomously knows it should form the hand)
41
Q

Why can an entire limb be regenerated when a blastema from the cut at the hand when transplanted onto the cut at the forelimb if the cells of the blastema will ONLY form the HAND?

A
  • Cells at the CUT site sense a discontinuity in the positional values (Between the transplanted blastema and the positional values of the cut site)
  • Cells are the cut site DE-DIFFERENTIATE to form the missing cells
42
Q

How do the proximal and distal cells in the blastema sort?

A

Via differential adhesion

43
Q

What is the experiment that shows that the proximal and distal cells in the blastema sort by differential adhesion?

What is seen?

How can this be interpreted?

A

Take blastema cells from the distal stump and proximal and co-culture them

Proximal cells ENGULF the distal cells:

  • Distal cells stick more tightly together
  • Proximal cells stick more tighter to the distal cells rather than themselves
44
Q

What happens if treat the blastema with the antibody against prod1?

A
  • Preferential adhesion is lost and the proximal cells stick better together than than to the distal cells
  • Cells don’t integrate
45
Q

What type of protein is Prod1?

A

A GPI linked protein

46
Q

What does RA do in the blastema?

What can this be used to do?

A

Reprogrammes it:

  • Can make a distal blastema a more proximal one
47
Q

What determines the characteristics of the blastema?

A

RA

Meis homeobox genes

48
Q

What happens to regeneration if the nerve is DESTROYED before amputation occurs?

What does this show?

A

No regeneration (which would normally regenerate if it wasn’t destroyed)

Shows:
- The nerve supplies some factor/protein that is required to DRIVE regeneration

49
Q

What happens if cut a limb that has NEVER seen a nerve?

A

Regeneration will occur

50
Q

What is the molecular explanation for the regeneration ONLY when innervated?

A
  • nAG (Newt anterior gradient) is expressed by the NERVE SHEATH in response to wounding
  • nAG can replace the limb in terms of outgrowth
  • nAG binds to prod1 (adhesion)
51
Q

Where is nAG expressed during development?

What happens to this expression following innervation?

What occurs in an aneurogenic limb?

A

In the epidermis of the embyro

Following innervation, nAG expression in the epidermis is down regulated

However, in an aneurogenic limb, this downregulation doesn’t occur:

  • Epidermis continuously expresses nAG
  • -> Provides a constant supply of nAG to drive outgrowth in the denervated limb
52
Q

How does insect regeneration occur?

A

Involves sensing the DISCONTINUITIES in the positional values which are created by amputation

Missing values are filled in IRRESPECTIVE of the overall structure (tissue only looks LOCALLY)

53
Q

What happens if cut between 4 and 5 of the leg of a host cockcroach and transplant to position 1?

A

Tissue senses that positions 1 and 5 shouldn’t be together

Responds by regenerating the missing parts 2,3,4

54
Q

What happens in a cockroach limb if cut between position 1 and 2 and transplant to a limb that has been cut between 4 and 5?

A
  • Tissue senses a position missing between 2 and 4
  • Regeneration of position 3
  • -> Mirror image of the limb
55
Q

What happens if transplant a mid tibia to a mid fibia in terms of regeneration?

Why?

A

No regeneration

Segments of the leg contain similar positional values

56
Q

What is the regeneration state of mammals?

A
  • Not good at regeneration but not FULLY INCOMPETENT

- Young children/mice can regenerate tips of digits, as long as you don’t cut beyond the nail bed

57
Q

Describe the regeneration in the peripheral nervous system

How is this done?

A

Axons CAN regenerate, as long as the neuron survives
But, neurons DO NOT regenerate

Use the Schwann cells as a GUIDE for their axons:

  • Regeneration occurs along the ORIGINAL pathway of the axon
  • Stimulates by Schwann cells along the way
58
Q

Describe the regeneration in the CENTRAL nervous system

Why?

A

Very LITTLE regeneration

Neurons TRY to send out new axons, but they collapse due to the NON-PERMISSIVE environment of the astrocytes and oligodendrocytes - prevent regeneration

59
Q

Why is neuron regrowth not wanted?

A

If constantly growing - would upset the system

60
Q

What does transplanting PNS Schwann cells into the CNS promote?

How?

A

Promote AXON GROWTH in the CNS

Positive factor from the Schwann cells?

61
Q

What structures of the body can regenerate?

A

Liver

Ribs

62
Q

When is the only point that ribs can regenerate?

A

As long as the peristeum is intact

63
Q

Describe heart regeneration in mammals

A

Doesn’t occur

64
Q

Describe heart regeneration in zebrafish

A

The VENTRICLE of the heart can be regenerated

BUT, not identical to embryonic heart development

65
Q

How can it be seen that regeneration of the zebrafish heart is not the same as in embryonic development?

A

By looking at molecular markers:

- msxB and C expressed in the regenerating heart but NOT in the embryonic heart

66
Q

What is regeneration of the heart driven by?

A

DEDIFFERENTIATING muscle cells

67
Q

What is regeneration NOT dependant on?

A

Not dependant on stem cells, dependant on de differentiation of EXISTING cells

68
Q

What 2 options can occur when there is damage?

A

Scarring OR regeneration

69
Q

What do mutants in msp1 in zebrafish show?

A

Scarring rather than regeneration

70
Q

How does regeneration in the zebrafish heart occur?

A

1) Blood clot form - closes off the ventricle
2) Endocard activated - expresses raldh2
3) Epicardial activation, which moves to cover over the wound
4) Neuregulin drives cardiomyocyte proliferation (increase in cell NUMBER, not size)
5) Newly formed muscle expresses FGF –> signals back to the epicard cells, stimulating them to INVADE the muscle and REESTABLISH blood vessel in the newly formed muscle
6) Clot dissolved

71
Q

How long does it take for the endocard to be activated?

A

Not very long, 6 hours

72
Q

What happens if miss express neuregulin in a NORMAL heart?

A

Drives PROLIFERATION

73
Q

When are mice able to regenerate their heart?

A

Neonatally - shortly lose this after birth

74
Q

What is the loss of the neonatal mouse being able to regenerate the heart correlated to?

A

The LOSS of neuregulin sensitivity:

- Doesn’t sense neuregulin, doesn’t enter the cell cycle

75
Q

What happens when express erbb2 in cardiomyocytes during regeneration of the mouse heart?

A

Better function/regeneration

Smaller scar volume, better functioning heart

BMS247 - Stem cells (15 decks)

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