9c.2 Regeneration

Question 1

Limb regenerationon in salamander

Answer 1

• Tissue-specific genes are down-regulated
• Genes associated with progress zone mesenchyme of embryonic limb buds are re-expressed (eg msx1,
which is abundant in limb bud mesoderm)
• The apical ectodermal cap (AEC) secretes Fgf8 protein, thus acts much in the same way as does the AER in embryonic limb development, although the AEC is about 10 x bigger than the AER!

Question 2

What fate does a dedifferentiated cell take one

Answer 2

Blastema cells retain their specification despite dedifferentiation. ells go back in journey only to re-dif as same cell as before

Question 3

nAG

Answer 3

•newt anterior gradient protein
•nAG normally supplied by limb nerve
•Limb is denerved (no nAG)
•7 d later amputed.
•5d later nAG is electroporated into the limb
blastema.
•Control newt not supplemented with nAG limb remained as a stump. Supplementation of nAG restored the ability to regenerate the limb.

Question 4

Cell moment in Hydra

Answer 4

• cells move around and can alter fate depending on number of days since development
• starts at top, then moves down till sluffed off from basal disk

Question 5

Bud location is likely determined by

Answer 5

Bud location is likely determined by the intersection of BOTH head AND foot inhibition gradients
•foot activation proteins: shinguard, a tyrosine kinase
•Where the level drops off, the bud forms!!

Question 6

Wnt signalling forms what in hydra

Answer 6

•Wnt establishes hypostome (part that has a mouth) acting through canonical B-catenin pathway

Question 7

What’s the Organizer in hydra

Answer 7

• Hypostome is the Organizer in hydra
• When transplanted hypostome can induce the host tissue to form a secondary axis.
• Hypostome produces both head activation and inhibition agents.
• Hypostome is the only self-differentiating region of hydra.
• Head inhibition signal suppresses the formation of new organization center.

Question 8

Grafing experiment- Indicate the presence of gradient:
•Hypostome from donor hydra inserted into the middle region of host hydra
•Tissue from basal (bottom) region of donor hydra inserted into the middle region of host hydra
•issue from hypostome and basal region of donor hydra inserted into the middle region of host hydra

Answer 8

1) Hypostome from donor hydra inserted into the middle region of host hydra. Hypostome induces secondary apical-basal axis.
2) Tissue from basal (bottom) region of donor hydra inserted into the middle region of host hydra. It induces secondary axis but with opposite polarity.
3) Tissue from hypostome and basal region of donor hydra inserted into the middle region of host hydra. It either fails to induce a secondary axis or weak induction is observed.

Question 9

Epimorphic Regeneration:

Answer 9

If the hydra is cut in
mid section then:
• Interstitial cells at the site of wound undergo apoptosis.
• Dying cells produce Wnt3a.
• Wnt3a induces β-catenin in the interstitial cells.
• This promotes proliferation of interstitial cells and there is remodelling of epithelial cells.
• Secondary axis is formed.

Question 10

Morphallactic regeneration:

Answer 10

Cut made close to head. Wnt 3 in the epithial cells repacern the tissue and no secondary axis formed.

Question 11

Compensetory Regulation in Hepatic regeneration

Answer 11

• Standard assay for liver regeneration is partial
hepatectomy (removal of a portion of lobe).
• Liver compensates for the removal of the tissue by enlarging and the mass equivalent to the removed tissue is regenerated back.
• compensatory regeneration is the recovery of the lost tissue by division of differentiated
hepatic cells.
• Liver cells don’t dedifferentiate

Question 12

Head inhibition gradient:
•Tissue from sub-hypostomal region is transplanted into the same region in intact host
•Tissue from sub-hypostomal region is transplanted into the same region in decapitated host
•Tissue from sub-hypostomal region is transplanted into the bottom region of intact host.

Answer 12

1)Tissue from sub-hypostomal region is transplanted into the same region in intact host no
secondary axis-head formed.

2) Tissue from sub-hypostomal region is transplanted into the same region in decapitated host a new secondary axis is formed.
3) Tissue from sub-hypostomal region is transplanted into the bottom region of intact host. Head forms lower down. Indicating the presence of head-inhibition gradient in the hypostome.

Question 13

There are 2 mechanisms of regeneration upon injury to liver

Answer 13

1. Differentiated mature cells that do not divide under normal are induced to divide.
   - There are 5 types of cells in the liver, including hepatocytes, ductal cells, fat-storing (Ito) cells, endothelial cells and Kupffer cells that begin proliferation and make more of themselves to make up for the missing part.
2. Quiescent hepatic progenitor cells, oval cells are activated to proliferate when hepatocytes are destroyed due to senescence, alcohol or disease.
   - Oval cells (small progenitor population)differentiate into hepatocyte or bile duct cells

Question 14

Injury is sensed by some of the hepatic factors missing or secreted in the blood stream triggering liver cells to divide.

Answer 14

• Kuppfer cells secrete IL-6 and TNF-α
• Stellate cells secrete hepatocyte growth factor (HGF) and TGF-β.
– HGF binds to its receptor c-Met that is increased immediately upon injury.
• Increased bile concentratoons in the blood activates Fxr transcription
factors that increase cell proliferation.