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Developmental Biology. > Limb Regeneration. > Flashcards

Limb Regeneration. Flashcards

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1
Q

What is limb regeneration?

A

The replacement of limb parts that have been lost or damaged.

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2
Q

Does limb regeneration require the expression of any new genes?

A

No.

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3
Q

What gene mechanisms do organisms use to regenerate their limbs?

A

By gene mechanisms that are already in place.

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4
Q

The same genes that are involved in limb bud outgrowth are involved in what?

A

Limb regeneration.

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5
Q

A single cell from a plant can develop into what?

A

A whole organism.

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6
Q

Can some organisms re-generate from small fragments?

A

Yes. E.g. Starfish.

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7
Q

Insects and arthropods can re-generate what?

A

Lost appendages such as limbs.

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8
Q

Fish can re-generate what?

A

Their fins and portions of their heart/

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9
Q

Do mammals or vertebrates have more variation in their re-development?

A

Vertebrates.

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10
Q

Newts and salamanders can regenerate what?

A

Limbs and the lens of their eye.

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11
Q

Which organisms have the most restricted form of development?

A

Mammals.

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12
Q

What can mammals regenerate?

A

Hair shafts.

Portions of the liver.

Finger tips.

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13
Q

Can nematodes regenerate?

A

No.

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14
Q

Organisms that can re-generate tend to be what kind of developers?

A

Regulative developers.

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15
Q

Why can regulative developers re-generate and mosaic developers cannot?

A

Because the cells in regulative developers can tell the new cells what to form.

The cytoplasmic determinants that allow for the development of mosaic developers are used up so cannot drive re-generation.

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16
Q

What are the 4 types of re-generation?

A

Stem cell mediated.

Epimorphosis.

Morphallaxis.

Compensatory.

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17
Q

What is stem cell mediated re-generation?

A

Stem cells in the affected tissue that have pluripotential will be able to differentiate down a path that regenerates the missing body part.

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18
Q

What are stem cells?

A

Self renewing populations of cells that can differentiate into a limited set of differentiated cells.

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19
Q

Give an example of stem cell mediated re-generation?

A

Hair re-growth from follicular cells.

Red and white blood cells can be regenerated by hematopietic stem cells.

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20
Q

What is epimorphosis?

A

Epimorphosis allows for the regeneration of amphibian limbs.

It will cause an outgrowth from the amputation point.

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21
Q

What is morphallaxis?

A

It re-organises the cells in the remaining tissue to form a short limb out of the available tissue.

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22
Q

What is compensatory re-generation?

A

This occurs in the mammalian liver.

It causes existing cells to replicate and replace cells that have been lost or damaged.

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23
Q

What organisms does epimorphosis take place in?

A

It takes place in planarians (flatworms) and amphibians.

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24
Q

How does epimorphosis affect differentiated cells?

A

They will have to revert back to a pluripotent state.

They will then re-differentiate and cause an outgrowth the makes a new, complete limb.

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25
Q

The French flag that is formed by morphallaxis is what size?

A

Much smaller.

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26
Q

How does morphallaxis work?

A

It leads to the re-patterning of existing tissues and the reestablishing of boundaries.

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27
Q

How does morphallaxis occur in planarians?

A

If a planarian is cut in half, the whole axis will be re-specified and the missing portions will form on each half.

This leads to 2 planarians with one half much larger than the other.

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28
Q

The French flag that is formed by epimorphosis is what size?

A

The same size.

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29
Q

How do hydra reproduce?

A

By budding.

Where offspring will grow out of the middle of the stalk of the old hydra.

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30
Q

What is the hypostome of a hydra?

A

The mouthlike region.

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31
Q

What happens if the hypostome of a hydra is transplanted to the middle of of a hydra?

A

The head portion of a new hydrostome grows out of the hydra.

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32
Q

The growing of a hydra out of the site of a transplanted hypostome is what form of re-generation?

A

Morphallaxis.

33
Q

What happens if the basal disc of a hydra is transplanted to the middle of of a hydra?

A

A new basal disc will grow out of the hydra.

34
Q

The basal disc and the hypostome of a hydra can lead to what?

A

They can induce an outgrowth of cells.

35
Q

If both the basal disc and the hypostome are transferred to middle of the hydra, what will happen?

A

Nothing.

36
Q

Why will nothing occur if both the basal disc and the hypostome are transferred to middle of the hydra?

A

Because the basal disc and the hypostome will inhibit each other.

37
Q

If a hypostome from a different hydra is transplanted near the head of another hydra, what will occur?

A

No growth.

Same thing occurs with the basal disc.

38
Q

If a hypostome is removed from a hydra and then a hypostome from a different hydra is transplanted on to the hydra that lost its hypostome, what will occur?

A

A new hypostome will form.

Same thing occurs with the basal disc.

39
Q

If a hypostome is transplanted from a hydra and placed by the basal disc of another hydra, what will occur?

A

A new hypostome will grow.

Same thing occurs with the basal disc.

40
Q

Why do the hypostome and the basal disc inhibit each other?

A

Because the hypostome and basal disc produce a gradient where growth of one is inhibited by proximity to the existing organ.

If the transplanted organ is moved towards the opposite end, then the inhibitory gradient is lower and budding can occur.

41
Q

Give an example of how the gradient effect of the hypostome and basal disc work?

A

If a basal disc is transplanted from a hydra to an area that is close to the basal disc of another then the basal disc that is already present will inhibit the growth of the other.

However if the transplanted basal disc is placed near the hypostome of a new hydra, then a new basal disc will develop.

42
Q

Why can baby hydras not reproduce?

A

Because they cannot bud as the gradients of the basal disc and hypostome are too close together.

When the baby hydra grows, the gradients will be further apart, allowing for an area where new hydra can bud out of the old hydra.

43
Q

Limbs in amphibians can re-generate via what method?

A

Epimorphosis.

44
Q

The cells involved in limb re-generation via epimorphosis in amphibians must be able to do what?

A

The cells in the region that were not amputated must be able to re-differentiate and become pluripotent.

Then they must re-differentiate again to form a new limb.

45
Q

What is step 1 of re-generation of an amphibian limb?

A

Rapid migration of epithelial cells to cover the wound.

46
Q

What is step 2 of re-generation of an amphibian limb?

A

There is thickening of the epidermis to form the apical epidermal cap (AEC).

47
Q

What is step 3 of re-generation of an amphibian limb?

A

The blastema forms and cells de-differentiate.

The AEC will send FGF to the newly pluripotent cells beneath the the wound surface, this causes proliferation which forms the blastema.

48
Q

What is step 4 of re-generation of an amphibian limb?

A

Growth of the blastema.

49
Q

What is step 5 of re-generation of an amphibian limb?

A

The cells differentiate into different roles.

50
Q

What is the AEC?

A

It is similar to the apical ectodermal ridge.

51
Q

What is the blastema?

A

It is similar to the progress zone.

52
Q

Growth of the blastema depends on what?

A

Factors that are produced by the AEC and nerves.

53
Q

Which cells will not differentiate into different roles during the re-generation of an amphibian limb?

A

Nerves cells.

54
Q

Differentiation during the re-generation of an amphibian limb is guided by what genes?

A

The HOX genes.

55
Q

What happens after 2 days of amphibian limb regeneration?

A

Skin and muscle will regress from around the humerus and the wound is covered.

56
Q

What happens after 5 days of amphibian limb regeneration?

A

A thin accumulation of blastema cells is seen beneath a thickened epidermis, this is the AEC.

57
Q

What happens after 7 days of amphibian limb regeneration?

A

A large population of mitotically active blastema cells lie distal to the humerus.

58
Q

What happens after 8 days of amphibian limb regeneration?

A

The blastema elongates by mitotic activity, de-differentiation has occurred.

59
Q

What happens after 9 days of amphibian limb regeneration?

A

Early regeneration can be seen and chondrigenesis has begun.

60
Q

If nerve cells are removed from a salamander limb, will re-generation occur?

A

No.

Unless it is placed in a bath of FGF 2.

61
Q

What role is it believed that the nerve cells have in the re-generation of the limbs?

A

That the nerves create a stimulus that starts regeneration.

They secrete FGF and it is thought that they may secrete other growth factors such as transferrin or glial growth factor.

62
Q

Can frogs re-generate limbs?

A

No.

63
Q

Why can frogs not re-generate limbs?

A

Because they cannot secrete FGF 10.

64
Q

How can limb re-generation occur in frogs?

A

If we stimulate it by adding FGF10.

65
Q

When FGF 10 is used to stimulate re-growth of the limb in a frog, how does it work?

A

IT induces FGF 8 and causes limb outgrowth and regeneration.

This means that the program for regeneration is still there, but the activation has been lost.

66
Q

What genes will program the regeneration of the limb by telling cells what to become when they grow?

A

The HOX genes.

67
Q

If the limb is amputated at the wrist from a salamander and that salamander is placed in a bath of retinoic acid, what will happen?

A

The HOX genes are reprogrammed and a whole new arm will grow out of the wrist.

This is because the HOX genes are not giving the correct positional information.

68
Q

In mammals, what is process that occurs when a limb is lost?

A

Injury occurs.

Wound closure by epithelial cells.

Cells proliferate.

Proliferation stops.

Wound is healed.

69
Q

In organisms that can re-generate, what is process that occurs when a limb is lost?

A

Nerves release FGF causing proliferation/ de-differentiation.

AEC Forms.

Blastema forms.
Regeneration occurs.

70
Q

What happens once the lens is lost from eye of a salamander?

A

Once the lens is removed, the iris tissue will proliferate and de-differentiate and start to divide.

Outgrowth will then occur and differentiation will determine the new roles of the cells.

71
Q

What happens 10 days after the lens is lost from the eye of a salamander?

A

The de-differentiated cells will grow and form a vesicular lens rudiment.

72
Q

What happens 12-16 days after the lens is lost from the eye of a salamander?

A

The internal layer of the lens vesicle will thicken and synthesis of the crystalline begins.

73
Q

What happens 25-30 days after the lens is lost from the eye of a salamander?

A

Lens regeneration is complete.

74
Q

How can newts re-generate their retina?

A

Via the retinal pigmented epithelium.

If the retina is damaged, then the retinal pigmented epithelium will de-differentiate and grow out and differentiate to form a new retina.

75
Q

Can infant humans re-generate finger tips?

A

Yes. As long as there is some fingernail left.

If the wound is sutured then no regeneration occurs.

76
Q

How can fin re-generation occur in fish?

A

By the exact same method as limb regeneration.

77
Q

Are there nerves involved in fin regeneration in fish?

A

No.

78
Q

Where must the amputation be if fin regeneration is to occur in fish?

A

Above the bones in the fin.

Developmental Biology. (21 decks)

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