Regeneration ppt

1. REGENERATION

2.  INTRODUCTION.
 MECHANISM OF REGENERATION.
 EPIMORPHIC REGENERATION OF SALAMANDER
LIMBS.
• Formation of the apical ectodrmal cap & regeneration
blastema.
• Proliferation of the blastema cells: The requirement
for nerves & the AEC.
• How do the blastema cells know their proximal and
distal levels.

3. Regeneration is the reactivation of development in
postembryonic life to restore missing tissues.
• The ability to regenerate lost part is present throughout the
animal kingdom but to various extent.
• Among invertebrate regeneration power is especially more in
sponges, coelenterates, flatworms, & tunicates.
• Among vertebrates the power of regeneration is limited to the
regeneration of limbs, jaws , gills & tail while in higher
vertebrates it is limited to healing of damaged tissue only.

4. Regeneration does in fact take place in different species
& can occur in four major ways:
1. Stem-cell mediated regeneration: stem cell allow an
organism to regrow certain organs or tissues that have been
lost. Examples: continual replacement of blood cells from
the hematopoietic stem cells in the bone marrow.
2. Epimorphosis: In some species, adult structure can undergo
dedifferentiation to form a relatively undifferentiated mass of
cells that redifferentiates to form the new structure .
Example : planarian flatworm regeneration & regeneration
of amphibians limbs.
3. Morphallaxis: Here, regeneration occurs through the
repatterning of existing tissues, & there is little new growth.
Example: regeneration in Hydra.

5. 4. Compensatory regeneration: Here, the differentiated cell
divide but maintain their differentiated functions. Each cell
produce cells similar to itself ; no mass of undifferentiated
tissues forms. This type of regeneration is characteristic of the
mammalian liver.
Epimorphic Regeneration of Salamander Limb
• Salamander accomplish epimorphic regeneration by cell
dedifferentiation to form a regeneration blastema .
• The blastema arise from the originally differentiated tissues –
which then proliferates & redifferentiates into the new limb
part. Bones, dermis & cartilage just beneath the site of
amputation contribute to regenerating blstema.

6. Distal amputation Proximal amputation
Original
limb
Amputation
7d
21d
25d
32d
42d
72d
Regeneration of
Salamander
Forelimb.
In both instance
, the correct
positional
information was
re-specified & a
normal limb was
regenerated
within 72 days.

7. Formation of the apical ectodermal cap &
regeneration blastema
• Epidermal cells from the remaining stump migrate to cover the
wound surface, forming the wound epidermis.
• During the next 4 days, the extracellular matrices of the tissues
beneath the wound epidermis is degraded by proteases,
liberating single cells that undergo dramatic dedifferentiation.
• Bone cells, fibroblasts, & myocytes all lose their differentiated
characteristic & becomes undifferentiated mesenchyme cells.
• This cell mass is the regenerating blastema, after the
mesenchymal cells have formed the blastema, the developing
appendage assumes a conical shape.

8. • The wound epidermis thickens to form the apical epidermal
cap (AEC), which act similarly to the apical cap of the
embryonic limb bud.
(A) (B) (C)
Regeneration in larval forelimb of the spotted salamander
Ambystoma maculatum .
2 days 5 days 7 days

9. (D) 8 days
(E) 9 days (F) 10 days
A- apical mesenchyme
U- ulna
R- radius
P-stump where the
amputation was made
D1 & D2- two digits
H- humerus
C(ankle)- the
precartilaginous
condensation for carpal
bone.

10. Proliferation of the blastema cells:
The requirement for nerve & the AEC
• The growth of the regeneration blastema depends on the presence
of both the apical ectodermal cap & nerves.
• The AEC stimulates the growth of the blastema by secreting Fgf8
(just as the apical ectodermal ridges does in normal limb
development). But the effect of AEC is only possible if nerves are
present.
• Regeneration of newt limb depends on newt anterior gradient
protein (nAG).
• This protein can cause blastema cell to proliferate in culture, &
it permits normal regeneration in limbs that have been
denervated.

11. (A)
(B)
Regeneration of newt limbs
depend on nAG
(A)The limb is denervated
& a week later is amputated.
After 5 days, nAG is
electroporated into blastema.
(B) Result: denervated
amputated limb remain
a stump.
if, (not giving nAG).
The limb that is given nAG
Regenerates tissue &
proximal- distal polarity.

12. How Do the Blastema Cells Know Their Proximal and
Distal Levels ?
• The anterior-posterior axis is established by Sonic hedgehog
activation & the graded expression of the HoxD series of genes.
• The proximal-distal axis is reestablished using retinoic acid (RA),
HoxA genes, & fibroblast growth factors, just as in the
developing limbs.
• The retinoic acid is synthesized in the wound epidermis of the
regenerating limb & forms a gradient along the proximal-distal
& anterior-posterior axes of the blastema.
• This RA gradient inform cells of their position along that axis in
the limb.

13. Gilbert, S.F. Developmental Biology. 10th ed.
Sunderland, MA: Sinauer Associates, 2010.