L7 - Regeneration Flashcards
Is regeneration linked to the complexity of an organism
No
Thinking about the French flag model if there was the left hand portion removed what types of regeneration could occur
Morphallaxis
Epimorphosis
What is morphallaxis
Little change in the number of cells
Cells present acquire new fates
What is epimorphosis
Formation of a growth zone and proliferation occurs
What mechanism of regenration is seen in Hydra
Mophallaxis
Morphalaxis may also be known as
“regeneration without ______”
Growth
Describe the basic organisation in hydra
Simple
Two germ layers (no mesoderm)
Simple mouth - hyposostome surrounded by tentacles and an elongated body column
Describe growth in Hydra
Grows continuously meaning that cells must change their positional values
During regeneration of the head how many gradients form - what are they
2 gradients
1) Positional value
2) Head inhibitor gradient
What does the positional value determine
Head inducing ability
Resistance to the inhibitor
Describe what is seen when head cells are transplated into the body
Why
Nothing is seen
Head inhibitory graidient is too high for head strucutres to develop
Describe what is seen when head cells are transplanted into the upper body of a HEADLESS ORGANISM
Development of head structures as there is no source of head inhibitor
Describe what happens when you transplant cells from the head region into the lower body (close to the basal disc)
Head inhibitor close to the basal disc is too low
Head strucutres are able to form
How long does it take for a piece of region 1 to induce a secondary axis
How long does it take for a piece of region 5 to induce a secondary axis
6 hours
30 hours
What signalling pathway is thouhgt to determine positional value
Wnt B-catenin
How was it seen that Wnt signalling was thought to determine positional value
Inhibition of GSK3 leads to a build up of B-catenin in the nuc
All regions acquire characteristics of the head organiser
What organism regenerated by epimorphosis
Urodele
Regeneration depends on
The posiiton of the cut
E.g. distal cut only distal strucutres regenerated
What is epimophosis
Regeneration by the growth of more tissue
What is the first thing to occur following amputation
Migration of epidermal cells
REGENERATION IS DEPENDENT ON THIS HAPPENING!
What happens to cells which are below the epithelum
Dedifferentiation forming a blastema
Muscle cells are multinucleis what is required for them to revert to uninucleate
Thrombin CRUCIAL
What is the blastema formed of
Dermis but can also be from dedifferentiated muscle and cartilage
Is there much transdifferentiation during blastema fomration
NO everything remains true to type except
dermis can form cartilage (and vice versa)
What are the (4) rules of regeneration
Limb regeneration always occurs distal to the wound
Regeneration occcurs appropriate to the positional value at the site of the cut
Not just a case of replacement of the missing parts
Morphogenic autonomy after transplant
Describe what would be seen if the hand was amputated and the limb was inserted into the belly - vascualr connections est an humerus cut
Regeneration starts from the proximal and distal surfaces of the humerus
Both proximal and distal surfaces regeneerate distal structures
How may proximal and distal blastema cells sort
Differential adhesion
What signalling molecule has been shown to proximalise a blastema
How does this work
Retinoic acid
Resets the positional value to that of a more proximal value
What is the mechanism for the proximalisation of the blastema through RA
Upregulation of meis homeobox genes of a GPI linked Prod1
What is the requirement for innervation
Regeneration depends on the presence of a nerve - unless a nerve wasn;t present in the first place
What is newt anterior gradient
A protein that can replace the nerve in supporting outgrowth
The mechanism of insect appendage regeneration involves the sensing of ….
Disscontinuities in positional values - missing positional values are then fill in irrespective of the overall strucutre
Describe what regeneration can be seen in mammals
Young children and mice can regenerate the tips of the digits
Describe regeneration in the PNS
Axons are able to regrow (but not whole neurones)
Describe regeneration in the CNS
Very little regenertion since the CNS is a non permissive enviro
Inhibitory myelin
Describe mammalian heart regeneration
Cardiomyocytes are present but dont divide
Progenitors present but aren’t used
Scar/maladaptive hypertrophy
Describe the ventricular regenerating in zebrafish
Not identical to emb dev in the head e.g. msxB and msxC
Regen dep on dediff muscle cells
Endocardium/epicardium involved
Neuregulin may be a signal from the epicardium
