Regeneration

Question 1

How can regeneration occur?

Answer 1

1. Stem cell mediated regeneration Stem cells allow an organism to regrow certain organs or tissues that have been lost, (replacement of red blood cells) 2. Epimorphosis Adult structures can undergo de-differentiation to form a relatively undifferentiated mass of cells which undergo re-differentiation 3. Morphallaxis Regrowth occurs through the repatterning of existing tissues (Hydra) 4. Compensatory regeneration Differentiated cells divide but maintain their differentiated function (mammalian liver)

Question 2

How does regeneration occur in flatworms?

Answer 2

Stem cell mediated regeneration in Planarians, which reproduce by binary fission. The cells capable of this and regeneration are the same pluripotent stem cells. The gradient along the flatworm was proven by showing the flatworm can regenerate its head and tail if the segment was large enough.

Question 3

Which cells form the new head or tail in Planarians?

Answer 3

The regeneration blastema forms from pluripotent stem cells called clonogenic neoblasts, which serve as stem cells to replace the aging cells of the adult body. They migrate to wound sites and regenerate the tissue. Can destroy all the dividing cells and transplant a single neoblast cell. This can restore all cells and any future planaria consist entirely of the genotype of the donor neoblast.

Question 4

How is polarity of Planarians known?

Answer 4

The dorsal ventral axis of regenerating cells is regulated by BMP and its inhibitors. BMP expression defines the dorsal region. The anterior posterior axis seems to be regulated by Wnts and B-catenins. B-catenin is activated by Wnts in the posterior facing blastema. Repressors of Wnt signalling prevents B-catenin production in anterior facing blastema.

Question 5

Epimorphic regeneration of salamander limbs?

Answer 5

The limb manages to only regenerate the missing parts.
Cell de-differentiation to form a regneration blastema, which then proliferates and re-differentiates into the correct limb parts.

Bone, dermis and cartilage just beneath the amputation site contribute to the blastema, as well as satellite cells from nearby muscle cells.

The cells differentiate back to their original cell type.

Epidermal cells migrate to wound site to form the wound epidermis. No scar forms.

Cells are liberated by degradation of extracellular matrices to allow for de-differentiation.

Genes which are expressed in differentiated cells are downregulated whilst genes associated with the proliferating progress zone of the embryonic limb have dramatically increased expression.

Question 6

Sources for new cells in regeneration?

Answer 6

1. Stem cells can self renew or turn into cell type
2. Differentiated cell enters cell cycle and creates same cell type
3. Can trans-differentiate
4. Pluripotent stem cell can make several cell types, found in animals capable of whole body generation

Question 7

Regeneration in Hydra?

Answer 7

Single cells can form Hydra even after “blending”.

Morphallaxis - remodelling occurs when only the apical head is lost.

Epimorphic response - cells proliferate when the basal head is lost (more cells are lost).