VL 12: Zebrafish Regeneration and Reprogramming

Question 1

Regeneration def.

Answer 1

Regeneration describes the replacement of a lost or damaged tissue, which includes the structural and functional restoration of the organ.
e.g. Starfish, Salamander, Antlers of deer

Regenarative capacity is very limited in mammals!

Question 2

Regenerator mechanisms

Answer 2

1) Regeneration via stemm cells e.g. Axolotl
2) Dedifferentation (epimorphic regeneration) & Redifferentation
3) Transdifferentiation
* Direct transdifferentation (purple) ; Unipotent -> Unipotent
* Transdifferenattion through a less-differentaited intermediate (mit Zwischenschritt)

Pic
Dedifferenation (yellow):
Unipotent (Differented cell types) -> Multipotent (Adult stemm cells)

Redifferentation (bright yellow):
Multipotent -> Unipotent

Through changes in:
- Gene expression (progenitor-specific genes)
- Proliferation capacity
- Cellular function

Not tissue or species specific

Question 3

Fin regeneratin in Zebra fish

Answer 3

Fin regeneration occurs through epimorphic regeneration (dedifferentiation).
* Can be proven by the Upregulation of progenitor-specific genes
* Cells maintain linage restricion= remeianing osteoblast gives rise to new osteoblast
* De- and redifferentiation of osteoblasts require dynamic retinoic acid (RA) signalling

Osteoblasten specialized bone cells, from emryonic mesemchyhme. -> synthezie the collagenous bone matrix

Question 4

Spinal cord regeneration in Zebrafish

Answer 4

Involves glial bridging
* Glial cells are a type of cell that provides physical and chemical support to neurons and maintain their environment.
* Injury response -> bridging glia, followed by Neurons -> Remodeling with Ependymal cells
* Ctgfa is required and sufficent to induce glial bridging

Ctgf a- Connective tissue growth factor a

Question 5

Retina regeneration in Zebrafish

Answer 5

1. Damage: Ablated photoreceptors
2. Activated Muller Glia (M.G:) (24hpi)
3. Dedifferentation: Reprogrammed M.G. (72 hpi)
4. Progenitor Migration and Differentation (96hpi)
5. Regenerated photoreceptrors (2-3wpi)

Factors needed:
* HB-EGF is necessary and sufficinent for Müller Glia Dedifferentation -> required for proliferation
* pan-metalloproteinase (MMP) inhibitor GM600 -> Prevents HB-EGF-shedding

HB-EGF: Heparin-binding EGF-like growth factor

Question 6

Herat attack- Cardiac injury in mammals (2 Problems)

Answer 6

1) O2-loss causes death of cardiomyocytes
* Adult cardiomyocytes cannot proliferate

2) Fibrotic tissue accumulates at the wound
* the fibrotic scar cannot be degraded

-> mammalian hearts fail to regenerate/heal

Question 7

The zebrafish herat regenerates! How?

Answer 7

If the zebrafish heart gets injured, a initial fibrin clot forms at the wound site, which is replaced by cardiac muscle in 1-2 month.

1) Inflammatory Phase (1-3 dpi)
* Inflammatory cell infiltration
* Activation of endocardium and epicardium
* Outside cells (Epicardium) engulfs whole scar area

2) Reparative phase (3-14dpi)

• Cardiomyocyte proliferation: pre-existing cardiomyocytes undergo limited dedifferentiation to facilitate proliferation
  –> start to divide and redifferentiate to replace tissue
• Fibrotic tissue deposition (myofibroblasts): Fibroblasts (growth factor) is produced and docs into epicardial cells. Epicardial cells + Fibroblast march into myocardium and vasculatizes it -> new muscles

3) Regenerative Phase (14-…dpi)
* Fibrotic tissue removal

Question 8

BMP signalling- required for regeneration

Answer 8

BMP signalling
* is active in border zone cardiomyocytes
* is required for regeneration
* regulates cardiomyocyte dedifferentiation
* is required for myocardial proliferation

Question 9

Il-11 in injured zebra fish tissue

Answer 9

Il11 signaling
* is required for heart and fin regeneration
* functions from the endocardium to regulate: Myofibroblast differentation (fibrosis) & Cardiomyocyte repopulation at the injury

Question 10

Why Study regeneration in the zebrafish embryo/ larva?

Answer 10

-tissues repair after an injury: Allows to study the immune system response on an injury
-high number of animals can be used
-regeneration is faster
-embryos are transparent, live imaging is possible
-chemical treatments (screens) are more feasible

Cellular reprogramming –> a potent tool in regenerative medicine.