#salamander

Regeneration -lll

Salamander limb regeneration occurs by:

Salamander limb regeneration occurs through epimorphosis characterized by histolysis, dedifferentiation, formation of regeneration blastema, extensive proliferation, and re-differentiation recapitulating developmental programs. After amputation wound epidermis forms apical epidermal cap expressing FGF8, Wnt, BMP modulators, nerves provide trophic factors inducing MMP degradation and cell-cycle re-entry. Blastema accumulates multipotent progenitors restoring missing portion distal to cut. This contrasts morphallaxis where existing tissues repattern without growth, compensatory hypertrophy, or simple stem-cell renewal. Molecularly re-activation of FGF10-FGF8, SHH-Gremlin loops indicates redeployment of limb development pathways during epimorphic regeneration.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Salamander limb regeneration as epimorphic mechanism.

View Details

Regeneration -lll

Salamander limb regeneration proliferation is dependent on:

Axolotl limb blastema proliferation and formation depend absolutely on nerve presence providing trophic factors. Denervated limbs after amputation fail to form blastema, undergo fibrosis. Nerves supply FGF2, neuregulin, BMP, anterior gradient protein nAG, maintain apical epidermal cap expression of FGF8 and Wnt5a, prevent differentiation. Accessory limb model demonstrates sufficient nerve fibers diverted to wound plus skin graft induces ectopic blastema without amputation. Molecularly nerve signals activate blastema cell cycle, sustain Myc and maintain MMP activity degrading matrix. Hence limb regeneration proliferation is nerve-dependent distinguishing salamanders from nerve-independent regeneration in other species.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Nerve dependence of salamander limb regeneration and proliferation.

View Details

Regeneration -lll

What structure maintains positional information during limb regeneration in salamanders?

During salamander limb regeneration blastema itself carries and maintains positional information acquired from stump level. Cells retain memory through persistent expression of Meis1/2, HoxA9, HoxA13, and cell surface protein Prod1 gradient correlating with proximal-distal origin. Transplantation of proximal blastema to distal location results in intercalation, distal to proximal does not unless proximalized by RA. Blastema sorting assays demonstrate differential adhesion based on Prod1 levels preserving positional disparity. Therefore blastema constitutes repository of positional identity integrating retinoid and FGF cues ensuring regenerate restores correct pattern with faithful proximal-distal polarity.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Blastema maintains positional information via Prod1 and Meis.

View Details

Regeneration -lll

Salamander limb regeneration involves:

Axolotl and newt limb regeneration proceeds via epimorphosis requiring wound epidermis, nerve-derived trophic signals, immune modulation. Stump tissues including muscle, dermis, cartilage, Schwann cells undergo dedifferentiation to lineage-restricted progenitors accumulating beneath apical epidermal cap as blastema. These multipotent progenitor cells proliferate driven by FGF8, FGF10, BMP, Wnt signaling, maintain positional memory via Prod1, Meis, Hox gradients, then redifferentiate reconstructing missing limb. Nerve deviation experiments show blastema formation depends on threshold neurotrophic support, demonstrating complex orchestration of growth factors, extracellular matrix remodeling, and re-deployment of developmental programs.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Salamander limb blastema formation and multipotent progenitors.

View Details