Diff12 - 33 Flashcards
What are the two forms of regeneration possible?
Morphallaxis and epimorphosis
What is morphallaxis?
Repatterning without growth
What is epimorphosis?
Regeneration by regrowth
What can urodele regenerate?
Dorsal crest, limbs, retina, lens, jaw, tail
What is special about urodele lens regeneration?
Occurs from iris - cells need to transdifferntiate
What kind of regeneration does urodele exhibit?
Epimorphosis
What is essential for urodele regeneration?
Epithelial cells migrate over the wound surface
What is important to realise about urodele regeneration?
System for regeneration MUST be different to generation in ebryogenesis - otherwise the morphogens would have to magically act over a 10x larger distance!
What is the name of the regenerating front?
Blastema
What does de-differentiation of muscle cells require?
Local activation of thrombin, msx expression, Rb inactivation
Are cells truly dedifferentiating in the blastema?
No - muscle cells only become muscle, Schwann only Schwann; Sort of - dermis can become dermis OR cartilage
According to what rules does urodele regeneration occur?
All regeneration always distal to wound, according to positional value at the site of the wound; regeneration is dependent on innervation unless the limb never had a nerve
How does the wound blastema decide what to regenerate?
Reads loacl positional value and generates more distal positional values - it does not determine what is missing
What is thought to be important in positional value in limbs?
Cell adhesion
Why is cell adhesion thought to be important in positional value in limbs?
If distal is combined with proximal blastema, proximal engulfs distal, inferring distal self-stick and proximal stick more to distal than self
What is capable of manipulating positional value in limbs?
Retinoic Acid (RA)
Characterise the effects of RA
Dose dependent - more = more proximal generated
How might proximilisation by RA occur?
Upregulation meis homeobox genes and/or prod1
What is prod1?
Protein expresed at the highest level in the proximal regenerating blastema - induced by RA treatment
Why can limbs never innervated still regenerate?
It was shown that a molecule called newt anterior gradient (nAG) can rescue regeneration of denervated limb
What is interesting about the drosophila heart?
Ventricles can be regenerated
What is suggested to facilitate drosophila ventricle regeneration?
FGF
How does the drosophila ventricle regenerate?
Bleeding > blood clot > cardiomyocytic dedifferentiation and proliferation > epicardium covering of wound > new muscle express FGF > induces epicardial creation of new blood vessels to support new ventricle
What is the alternative method considered in heart regeneration?
Scarring
What regeneration occurs in mammals?
Tips of fingers, axons (if neuron survives), liver, ribs (if periosteum intact)
Why is neuronal regeneration so strictly regulated?
CNS is very delicate and elaborate - disrupted easily if regeneration was so easy
What germ layer are hydra without?
Mesoderm
How do hydra maintain body size?
Loss of cells through basal disc (end of tentacle) and asexual budding
What is interesting about positional values in hydra?
They must continually change, as cells constantly move up the hydra
Outline the signal gradients in hydra
Positional value - 1 high, 5 low ability to induce head; head inhibitor - produced in head
What molecular mechanics are thought to be involved in hydra head patterning?
Wnt/Beta catenin
Where is Wnt expressed in hydra?
Head and activated regenerating tip
Outline the hydra Wnt pathway
Decreased GSK3-b > increased nuclear beta catenin > activation of Wnt
