Lecture 30 Flashcards
What is meant by regeneration
Regeneration is the possibility of a fully developed organism to replace organs or appedages by growth or repatterning
Regeneration isn’t linked to the complexity of an organism, T or F
T – C.elegans cannot regenerate whilst amphibians can
There are two different types of organ regeneration; morphollaxis and epimorphosis, describe the differences between these mechanisms
Morphollaxis is the regeneration by the re-patterning of the remaining tissue to reform the lost structure but just smaller than original. In contrast, epimorphosis is the regeneration whereby a growth signal triggers cells to divide and replace the lost tissue
Hydra are capable of regenerating via morphollaxis, explain how this occurs
Because of hydra’s simplicity as an organism they grow continuously. This means that in order to maintain size cells need to be lost. This occurs via shedding from the tentacle regions or when reproducing asexually via budding. The remaining cells are thus required to constantly repattern and change their fate. This enables the hydra to regenerate lost tissue
What makes hydra so simple as an organism
They only contain two germ layers; the endoderm and ectoderm (don’t possess a mesoderm)
There are the two gradients present in the Hydra that determine regeneration and repatterning, one of which is the positional value gradient. Explain the role of this gradient in regeneration
The positional value gradient provides the cells a positional value depending on their distance down the body column from the head. This gradient determines the head inducing ability of the cells and encodes for resistance to a head inhibitor
What is the other gradient present in Hydra involved in regeneration
The head inhibitor gradient which decreases with the distance from the head
The positional value of the cells in the Hydra body is sufficient to allow formation of the head, T or F
F – the positional information is not sufficient
Why does grafting of Hydra head tissue into another hydra body column not lead to the development of a secondary axis and head structure
The presences of the head inhibitor gradient in the recipient prevents head structure formation
Explain the evidence that indicates there is a gradient that is preventing head formation in the hydra body plan
Decapitation of the recipient before grafting the other head leads to the generation of head structure from the graft. Similarly, distal grafting of the head in the recipient body plan is also sufficient to lead to development of the head
Explain the role of wnt/?-catenin in Hydra head formation
Wnt is expressed in the hydra head as well as in the regenerating tip. Inhibition of GSK3-? leads to upregulation of nuclear ?-catenin and thereby to activation of the Wnt pathway. Inhibition of GSK3-? in all regions of the body results in them all acquiring characteristics of the head organiser
Hydra ?-catenin can also induce a secondary axis in Xenopus embryos, what is the significance of this
Hydra and Xenopus organising centres arose very early in evolution. It is also likely that vertebrates evolved from animals with a simple body plan like that of hydra
What is meant by a urodele
Tailed amphibian (the masters of regeneration)
Give examples of structures that urodeles can regenerate
Dorsal crest, retina, lens, jaw, limbs and tail
Some regenerations require changes in germ layer. What is this referred to as
Trans-differentiation
What seems to be the main pattern of regeneration in urodeles
De-differentiation of some of the cells to re-pattern and regrow the tissue
What is the essential step in urodele limb regeneration
Migrations of epidermal cells over the wound surface. Signals from the epidermis drive regeneration
During limb regeneration and once the wound has been covered, the cells beneath it dedifferentiate. What is the name of the structure formed by this dedifferentiation
Blastema
Which cells dedifferentiate in urodele limb regeneration
Cartilage, muscle and dermis
What is required for muscle cells to dedifferentiate
They must become mononucleate
Explain what is meant when it is said that urodele limb dedifferentiation is limited
Whilst the dermis can transdifferentiate to form cartilage and the cartilage can transdifferentiate into dermis, muscle cells are only capable of dedifferentiating and giving rise to muscle cells
What are the two rules of regeneration
Limb regeneration is always distal to the wound and regeneration occurs according to the positional value at the site of the cut
What is meant when saying a bastema has autonomy
The blastemal can regenerate the structures lost in a different location if a distal blastema is transplanted to a proximal wound. The site of the wound can sense a discontinuity in positional values between the distal blastema and the cut site. The remaining tissue can then be formed by intercalary growth
Explain the role of nAG in supporting outgrowth during limb regeneration if the neuron is kept intact
Newt anterior gradient (nAG) is a protein than binds to the prod1 transmembrane protein. It is expressed in the nerve sheath in response to wounding. Innervation in the limb leads to the downregulation of nAG whereas, in an anueronic limb there is persistent nAG expression
What is absolutely required for normal limb regeneration
Normal innervation
When can a limb regrow with innervation and why
If there was no innervation to the structure before hand, it can regrow without any
