Regeneration Flashcards
What are the differences between the lifespan of some of the cells in the body?
What are examples of these cells?
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)
What is regeneration?
The possibility of the FULLY DEVELOPED organism to replace ORGANS or APPENDAGES by growth or repatterining of the EXISTING tissues
Does the complexity of the organism determine if an organism can regenerate?
NO
- C.elegans are very simple but CANNOT regenerate
- Some lower vertebrates are very good at regenerating
What organisms can regenerate an entire organism from a FRAGMENT their body?
- Flatworms
- Starfish
- Hydra
What are the 2 types of regeneration that can occur?
1) MORPHOLLAXIS
2) EPIMORPHOSIS
What is morphollaxis?
Repatterining WITHOUT growth:
- No changes to the cell number
- Shift in the fates of the cells already existing –> regenerate positional values
What is epimorphosis?
Regeneration by GROWTH:
How does epimorphosis occur?
GROWTH ZONE formed at the position of the cut
Growth zone then causes proliferation and regrows the MISSING PARTS of the structure
What is the structure of the hydra?
2 germ layers (endoderm and ectoderm)
How does the hydra regenerate?
By MORPHALLAXIS:
- NO growth
How does the hydra grow?
Continuously, with cells constantly changing their positional values
How do cells change their positional values?
By changing their FATES
What are the 2 gradients in the hydra that allow regeneration?
1) Gradient in POSITIONAL VALUE
- From the head region (pos. 1 being near the head)
2) HEAD INHIBITOR gradient
What does the PV of cells in the hydra determine?
Both:
- The head inducing ability (high at region 1)
- Resistance to the head inhibitor
What does the head inhibitor gradient do?
Forms a gradient along the body to prevent extra heads from forming
What happens when transplant a piece of region 1 tissue into region 3 of the body of a host hydra?
Why?
NOTHING HAPPENS
- Region 3 has high level os head inducer activity
- But level of the head inhibitor is high enough to prevent head induction
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?
Second head forms
No head inhibitor to prevent the formation of a second head
Where is head inhibitor released from in the hydra?
The head
What happens if transplant a piece of region 1 tissue into region 5 of the body of a host hydra?
Why?
Second head will form
Low levels of the head inhibitor
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?
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
What signals are important in forming a head organiser?
Wnt signalling
What happens with GSK3 inhibition?
What does this cause?
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
How is GSK3 inhibited?
Using Lithium
What is a urodele?
A ‘tailed’ AMPHIBIAN
How does regeneration in the urodele occur?
EPIMORPHIC:
- Through cell divisions making the new tissues
What can a urodele regenerate?
- Dorsal crest
- Limbs
- Retina
- Lens
- Jaw
- Til
Where does lens regeneration in the urodele occur from?
Why is this unusual?
What does this show?
From the iris
Unusual because the iris (neuronal) is a different germ layer to the lens (epidermal)
Shows that cells need to TRANSDIFFERENTIATE
What happens if resect the limb of the urodele?
Right structures are regenerated APPROPRIATE to where the cut is made
Where do the cells come from that allow tissues to regenerate in epimorphic regeneration?
Cells de-differentiate to reform the missing structures
What MUST happen for regeneration to occur in the urodele?
What happens if this is prevented?
Migration of the epithelial cells over the wound to close the wound
If prevented - NO regeneration