Practice question

Epimorphic regeneration involves formation of regeneration blastema via dedifferentiation or stem cell recruitment, extensive proliferation under wound epidermis, and patterning akin to developmental programs. Salamanders particularly axolotl exhibit textbook epimorphic limb regeneration: amputation induces wound epidermis becoming apical epidermal cap secreting FGF8 and Wnt5a, nerve signals release Newt anterior gradient protein, underlying dermis dedifferentiates forming Prrx1-positive progenitor blastema that grows and redifferentiates into cartilage, muscle, and connective tissue. Hydra uses morphallaxis without blastema, mammals and birds form scar tissue. Salamander epimorphosis provides paradigm for nerve dependence, positional memory, and growth control.