Lecture 2 Flashcards
What is regeneration
The replacement of lost body parts, restoring mass and/or function
What is homeostatic regeneration
the natural replacement of cells lost in day- to-day minor damage, cell death, and ageing
What is facultative regeneration
tissue replacement after substantial trauma like amputation or ablation
What happens after injury in lower vertebrates
adult cells can go “back to the future,” after injury, returning to an “embryonic” condition to begin the formation of new tissues and organs
What happens after injury in higher vertebrates
wound repair occurs after injury, resulting in fibrosis/scar formation.
What are three types of facultative regeneration + describe
Epimorphosis - de-differentiation, proliferation, re-differentiation, e.g. Salamander. retains form, mass, function
Morphallaxis - re-patterning without growth, e.g. Hydra. retains form, function
Compensatory regeneration - growth without re-patterning (not true regeneration) e.g. Liver. retains function, mass
Detail the process of limb regeneration in Salamanders.
After injury, a plasma clot forms, and within 6 to 12 hours, epidermal cells from the remaining stump migrate to cover the wound surface, forming
the wound epidermis. This single-layered structure proliferates to form the apical ectodermal cap. Cells beneath the cap undergo dedifferentiation forming a blastema.
Cell identity is remembered and the dedeffertiated cells only proliferate into the cells there were originally
Why are nerves essential for limb regeneration
Nerves release neural anterior gradient protein which is a ligand for Prod 1. Even if don’t have nerve cell but have nAG, limb regeneration occurs
Explain the importance of retinoic acid in the formation of limbs, and regeneration in Salamanders.
Retinoic acid gradients exist in development, with the proximal aspect of limbs exhibiting high
levels of retinoic acid, and distal aspect having low levels.
Retinoid acid expression controls Hox codes, which confer positional information
In Salamanders, when they have limbs
cut, the blastema develops a retinoic acid concentration gradient which informs development of
the new limb.
Blastemas can be proximalised through addition of exogenous retinoic acid, causing elongated limbs.
What happens when distal blastema put on proximal wounds eg proximal distal deletion
Proximal woustumpnd regernates limb, distal, distal stump restores hand and wrist, the limb is regenerated by intercalation.
The proximal blastema expresses high levels of RA coding for a proximal fate, while the distal blastema expresses low levels coding for a distal fate.
What happens when Proxima blastema put on distal wounds
When a proximal blastema is placed on a distal stump, a new arm forms from the wrist. The proximal blastema expresses high levels of RA indicating it is at a proximal site. There is no intercalation, elongated arm Is formed
What effect does exogenous retinoid acid have
Retinoic acid changes the positional values of the blastema. It proximalises the blastema.
A distal blastema will regenerate an entire limb in the presense of high levels of RA.
Proximal structures in the regenerated limb will come from the distal blastema
How does the liver regenerate? Why is this not true regeneration?
Compensatory regeneration. This involves proliferation of existing tissue, but no restoration in form
(and thereby function). There is no cell differentiation. Cells express embryonic transcription factors that increase cell division. Once the original mass of the liver is established, proliferation stops.
Hydra are freshwater cnidarians which are able to regenerate through morphallaxis. Describe the
process of morphallaxis.
Morphallaxis is where there is re-patterning of existing tissue. For example, is a hydra is cut in
half, there is no growth of tissue, but re-patterning of the two halves to form 2 smaller hydra.
What examples of morphallaxis exist in humans?
In
humans, the main example of morphallaxis is the hair follicle. (But this is not technically classified
as morphallaxis as it is not a human process.)
