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
