lec 26- limb regeneration Flashcards
what animals can regenerate limbs?
sea slugs, starfish, flatworms, axolotls, newts, and fish
what is the restricted regenerative abilities of mammals?
liver can regenerate, deer antlers can, broken bones can regen, cannot regenerate lost limbs but can regenerate lost tips of fingers
how does limb regeneration in amphibians occur?
-amputation of the limb is followed by a rapid migration of epidermal cells from the edges of the wound to form a covering over the surface of the stump = wound epidermis
-essential process for regeneration, if the stump is sutured, limb will not regenerate
-the blastema forms under the wound epidermis and gives rise to the new limb
-somehow positional info is conveyed to the blastema cells during regeneration
how does the blastema forms?
-it forms from cells beneath the wound epidermis, they lose their differentiated character and start to divide
-the blastema cells are derived from differentiated cells close to the amputation site
are all the blastema cells similar even though they can be from many different differentiated cells?
yes
can the blastema produce many different tissue types which eventually differentiate from it?
yes
what has the experiment found out on blastema cell types?
the cell types have limited potentials that are related to their origins in the embryo
do blastema cells from different limb tissues remain restricted to lineages related to their embryonic origin in the neurula stage embryo?
yes, e.g. cells derived from muscle can only form muscle
does the blastula know where the limb is amputated?
yes, letting it form normally
what experiment was done to show that regeneration depends on the site of amputation and not on tissues that are present in the limb?
-the hand was amputated from a newt and the remainder was inserted back in the newt
-another cut was made near the shoulder
-two arms formed from the open end new cut wound
how does regeneration occur according to he French flag model?
-the adult limb possesses a set of positional values along the proximal distal axis that are put in place during embryogenesis
-regenerating limbs read the positional values at the amputation site and restore all positional values distal to it
how is positional information converted to the regenerating limb?
by concentration of retinoic acid, high means more limb generated
are Hox genes and transcription factors also expressed in regenerating limbs?
yes
where does sonic hedgehog localize to in limb regeneration?
to both posterior limb buds and posterior blastema
what inhibits sonic hedgehog?
cyclopamine- acts by binding Smoothened and interfering with its function so that transcription is no longer activated even when hedgehog is around
how do the transcription factors help in limb regeneration?
-FGF8, FGF10, and Wnt are expressed in wound epidermis and blastema
-Wnt activates FGF
-blocking Wnt signaling stops FGF and blocks regeneration
