regeneration and stem cells

what are the basic steps of epimorphis regeneration?

1. Formation of the wound epidermis or apical ectodermal cap. (This is an essential step!) 2. The blastema forms under the wound epidermis. 3. Growth and re-patterning of the new tissue.

How does the regenerate know what needs to be made?

1. The growth of the blastema and the structures that it forms depend on the site from which it was taken, not the proximal structures. 2. The cells of the limb or tissue must retain some sort of positional information so they know where they came from in the limb

what are the 2 models of how the blastema forms and functions? (amphibians)

Old: Differentiated cell types undergo dedifferentiation to form a mass of multipotent stem cells New:relies on the production of proliferating cells from differentiated cell types, but the cells are not multipotent. They only differentiate into the cell type that they were from in the limb before the amputation

what induces dedifferentiation?(amphibians)

Production of a factor requires the activity of the protease thrombin

how does morphallaxis work?

Regeneration is achieved by re-patterning the existing tissue and re-establishing boundaries. -ex: hydra

what is the role of Wnt & FGF in blastema differentiation in fish?

Wnt & FGF is required for the process and that is does so in part by regulating cell proliferation.

what are pluripotent stem cells?

can differentiate into all cell types of the embryo but not extra-embryonic tissues like placenta. Ex. ICM of the blastocyst

what are the special criteria for accessory limb model of regeneration?

1. nerve has to be rerouted to the site of the wound. 2. if the wound is in the anterior part of the limb, tissue from the posterior part of the limb must be placed at the site of the wound. The boundary between anterior and posterior tissue appears to be essential for growth of the limb bc of positive feedback loop between FGF made by anterior cells and SHH made by posterior cells

what are the 4 types of regeneration?

1. stem cell mediated 2. compensatory 3. morphallaxis 4. epimorphis

what are the 2 main parts of the definition of a stem celll?

1. stem cells must exhibit potency or the ability to differentiate into specialized cell types. There are multiple levels of potency 2. the cell's capacity for self-renewal or the ability to divide numerous times while maintaining an undifferentiated state

what do the 2 basic models have in common?(amphibians)

Both models invoke the ability of differentiated cells of the injured limb to dedifferentiate into a stem-cell population that resides at the site of the wound under the wound epidermis

what is the blastema? (amphibians)

Forms under the WE and is comprised of what are believed to be stem cells.

what is the interaction between wound epidermis and blastema?

IGF from the blastema signals to the WE cells. This signal serves as a survival signal and induces the expression of Wnt5b --> promotes the expression of FGF20 and proliferation of the blastema

what are totipotent stem cells?

They can differentiate into any cell type, embryonic or extra-embryonic. Ex. morula @ 2-16 cells

what is the AEC and what does it do?(vertebrates)

apical ectodermal cap - similar functions to ARE in limb bud formation

how does epimorphis work?

depends on new growth, re-patterning, and re-establishment of boundaries. -ex: planaria and amphibian limbs

how does compensatory work?

differentiated cells divide to give rise to cells like themselves in order to replace damaged tissues. - ex: liver regeneration

in what direction does regeneration take place?

distal to the site of amputation

what is a somatic cell nuclear transfer? (Dolly)

egg from a donor is enucleated --> nucleus from a somatic cell is injected into the egg --> egg is re-activated and cell division begins --> embryo is implanted into a surrogate mother --> resulting lamb has DNA identical to the original donor

what is the accessory limb model of regeneration?

formation of additional limbs that grow out of a wound that is placed on the side of the limb, but only if special criteria are met

What establishes proximal-distal positional value?

retinoic acid. RA causes the distal blastema to adopt proximal positional value and form the structures appropriate for that positional value.

what are multipotent stem cells?

they can only differentiate into closely related cell types. Ex. adult stem cells such as hematopoetic stem cells, Paraxial mesoderm

how does stem cell mediated work?

utilizes stem cells to regrow lost tissues. - ex: blood cells, skin, hair shaft