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L2 Stem Cells > Regeneration > Flashcards

Regeneration Flashcards

1
Q

What are the 2 types of regeneration?

A
  • Morphallaxis
  • Epimorphosis
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2
Q

What is regeneration?

A

The ability of a fully developed organism to replace organs/appendages by growth or repatterning

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3
Q

Is the ability to regenerate linked to the complexity of the organism?

A

No

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4
Q

What is morphallaxis? (2)

A
  • No new cells/no growth
  • Existing cells change their fate to restore the patterning
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5
Q

What is epimorphosis?

A

New cells grow to replace the missing parts

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6
Q

What kind of regeneration is demonstrated in hydra?

A

Morphallaxis

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7
Q

What are the features of hydra? (4)

A
  • Only ectoderm and endoderm, no mesoderm
  • Head region and basal region
  • Split into positional values
  • Constantly losing and regrowing cells meaning cells are constantly adjusting to a new positional value
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8
Q

What 2 gradients are involved in head regeneration in hydra?

A
  • Gradient in positional value
  • Head inhibitor gradient
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9
Q

What does the gradient in positional value in hydra determine? (2)

A
  • Head inducing ability
  • Resistance to a head inhibitor
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10
Q

What is the head inhibitor gradient in hydra?

A

High levels of head inhibitor molecule is produced just below the head, diffuses down to inhibit head formation elsewhere

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11
Q

What is the evidence for a head inhibitor gradient? (3)

A
  • Graft a piece of tissue from just below the head onto the body of another hydra = no head formed because of the head inhibitor gradient in the recipient
  • Remove head from the recipient = remove the head inhibitor gradient = head forms from the transplant
  • Transplant the region to the basal area of the recipient = head forms because the gradient is weak at the basal end of the hydra
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12
Q

What is the evidence for the effects of positional value/head inducing capacity? (3)

A
  • Graft a piece of tissue from just below the head onto the body of another hydra = no head formed
  • Remove head from donor and wait a bit before transplanting = head forms in recipient because the cells have started to increase their positional value to restore the head
  • Remove more of the body from the donor and wait even longer before transplanting = head forms in the recipient again, needed to wait longer to increase their positional value
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13
Q

What signalling pathway is involved in determining the head region/top positional value? (2)

A
  • Wnt/beta-catenin signalling
  • Inhibition of GSK3beta (negative regulator of Wnt) causes nuclear accumulation of beta-catenin and induces head formation
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14
Q

What are the steps of limb regeneration in urodele (tailed) amphibians? (4)

A
  • Amputation
  • Epidermal cell migration to cover the wound
  • Cells below the epithelium dedifferentiate and form a blastema
  • Cells that dedifferentiate are dermis, cartilage and muscle
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15
Q

What makes multinucleated muscle cells dedifferentiate to perform limb regeneration? (3)

A
  • Thrombin (protease)
  • Msx1
  • Phosphorylated pRb (becomes inactive to allow regeneration)
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16
Q

How does regeneration differ to development? (2)

A
  • Involves different genes
  • Regeneration occurs on a much physically larger scale than development
17
Q

To what extent do cells dedifferentiate during regeneration? (2)

A
  • Only partial dedifferentiation
  • Some crossover between dermis and cartilage but cells mostly remain true to their type
18
Q

What are the rules of limb regeneration? (4)

A
  • Limb regeneration is always distal to the wound
  • Always according to the positional value at the site of the wound
  • Doesn’t simply regenerate the missing parts, regenerates everything that should be distal to the wound site
  • Blastema has the positional values encoded into it somehow and only regenerates what its meant to
19
Q

How is retinoic acid involved in regeneration? (2)

A
  • Determines the positional value of the blastema (proximal/distal)
  • Works via Rar delta 2, meis homeobox genes and upregulation of GPI linked protein prod1
20
Q

How does innervation affect regeneration? (2)

A
  • Denervation of limb before amputation prevents regeneration
  • A completely aneurogenic limb regenerates normally after amputation
21
Q

What is nAG? (2)

A
  • Newt anterior gradient
  • A protein which binds to prod1 and is expressed in the nerve sheath in response to wounding
22
Q

How is nAG involved in regeneration? (3)

A
  • Applying nAG to a denervated limb can replace the role of the nerve in supporting regeneration
  • Innervation of a limb during development switches off epidermal nAG which is why an amputated denervated limb doesn’t regenerate
  • An aneurogenic limb never has innervation so has persistent epidermal nAG expression
23
Q

How does limb regeneration occur in insects? (3)

A
  • Local sensing of discontinuity in positional values
  • Missing positional values are regenerated irrespective of the overall structure
  • Positional values are repeated in leg segments so graft of mid tibia to mid femur doesn’t cause regeneration of intermediate structures
24
Q

What are examples of mammalian regeneration? (5)

A
  • Young children/mice can regenerate the tips of digits after the nailbed
  • Axons can regrow in the PNS in the presence of Schwann cells
  • Very little regeneration in the CNS due to inhibition from glia, astrocytes and oligodendrocytes
  • Schwann cells from the PNS can promote axon regeneration in the CNS
  • Liver and ribs can undergo regeneration
25
Q

How does heart regeneration occur in mammals? (3)

A
  • Cardiomyocytes are present during damage but don’t divide
  • Progenitors are present but don’t perform repair
  • Scar formation and hypertrophy of the remaining muscle is maladaptive
26
Q

How does heart regeneration occur in zebrafish? (5)

A
  • Heart can be regenerated in a different process to during development
  • Relies on dedifferentiating muscle cells
  • Endo and epicardium signals are involved, epicardium covers the wound
  • Neuregulin from the epicardium signals to induce proliferation in the myocardium
  • Scar tissue forms if regeneration doesn’t occur effectively
27
Q

What is neuregulin?

A

A growth factor which is important for heart regeneration

L2 Stem Cells (12 decks)

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