1. Which organ systems are affected by amphibian metamorphosis? Describe briefly the
changes in these systems between larval and adult forms. What is initiating those
All changes are initiated by thyroid hormones thyroxin (T4) and triiodothryonine (T3). Travel
through blood to reach larva.
2. How would you define ‘regionally specific development programs’ (=organ specific
programmed response)? Give an example.
There are different tissue responses and timing of expression of various derivatives of thyroid
hormones. T3 or T4 hormones instruct limb bud muscles to grow and tail muscles to undergo
apoptosis. Organ specific programmed response is when there is specific responses to thyroid
horomone – tail transplanted onto trunk is still sensitive to apoptosis and re-absorption.
3. List and briefly describe three types of metamorphosis in insects.
Insect metamorphosis involves the destruction of larval tissues and replacement by entirely
different population of cells.
Ametabolous- no larval stage, direct development
Hemimetabolous- gradual metamorphosis
Holometabolous- larva, pupa, adult
4. List and briefly describe three main types of imaginal cells in insects. What is their role
Imaginal discs- form wings, legs, antennae, eyes, head, thorax, and genitalia
Histoblast nests- form adult abdomen
Imaginal cells within each organ-develop as larval organs degenerate
5. What are the four major regeneration mechanisms? Briefly (one sentence) describe
each of them. Epimorphosis- dedifferentiation into an undifferentiated mass followed by respecification
Morphallaxis- regeneration through re-patterning of existing cells
Compensatory regeneration- intermediate form
Stem cell mediated regeneration- regrowth of certain organs or tissues that have been lost
(continual replacement of blood cells)
6. Salamanders can reconstruct a complete limb, if necessary. Which parts of the limb are
getting reconstructed after amputation? How do we call this type of regeneration?
It only forms those parts that are missing none other. It is called dedifferentiation, proliferation,
7. Describe the process of limb regeneration in salamander.
Right after amputation a plasma clot forms. After the surrounding epidermis covers the wound,
wound epidermis. Wound epidermis is a single layer, it proliferates to form apical ectodermal
clot. No scar formation and no dermal closure like in mammals. Under cap dedifferentiation
and proliferation results in the regeneration blastema. Cell subsequently redifferentiate to form
8. What are the similarities between apical ectodermal ridge and apical ectodermal cap?
What are the differences? (Define both of them first.)
Apical ecotdermal cap require fgf10
9. What is the role of nerves in salamander’s limb regeneration?
Apical ectodermal cap is necessary: mesenchyme intergral to regeneration of limbs. Nerves
release factors that drive the proliferation of blastema cells
10. Explain the following statement: Blastema is heterogeneous population of restricted
Muscle cells only arise from old muscle cells and dermal cells only from old dermal cells.And
finally, cartilage from old cartilage or dermal cells. Blastema cells retain their specification.
11.What are the major steps in mammalian liver compensatory regeneration?
If a lobe from the liver is removed, it does not grow back; however, the remain tissue gets
bigger to compensate for the lost lobe. It is regeneration by proliferation and no
dedegeneration. Five type of liver cells divide to produce more of themselves, but they retain
their function. After the removal of the lobe the Hepatocytes that are connected to one another
do not respond to HGF (responsible for cells to return to cell cycle to produce of themselves).
The trauma activates metalloproteases that digest the ECM this leads to the separation and
the proliferation of hepatocytes. Liver stops growing at a certain size (unknown). There is a
second line of rengerative ability through oval cells which are prognitive cell populations. They
are activated once hepatocytes fail to regenerate the liver.
12.Define maximum life span. Define maximum life expectancy.
Maximum life spa