Which one of the following statements regarding limb regeneration in salamander is correct ?

Eduncle Best Answer

When an adult salamander limb is amputated, the remaining cells are able to reconstruct a complete limb, with all its differentiated cells arranged in the proper order. In other words, the new cells construct only the missing structures and no more. For example, when a wrist is amputated, the salamander forms a new wrist and not a new elbow. Experiments done with regeneration of a salamander forelimb showed that in the amputation made below the elbow and in the amputation through the humerus, the correct positional information was respecified in both cases. Hence statement A is correct.
        Salamanders accomplish this feat by dedifferentiation and respecification. Upon limb amputation, a plasma clot forms, and within 6 to 12 hours, epidermal cells from the remaining stump migrate to cover the wound surface, forming the wound epidermis. This single-layered structure is required for the regeneration of the limb, and it proliferates to form the apical ectodermal cap. Hence statement B is incorrect.
        The formerly well-structured limb region at the cut edge of the stump forms a proliferating mass of indistinguishable, dedifferentiated cells (Hence not progenitor cells, which makes Statement C also incorrect) just beneath the apical ectodermal cap. This dedifferentiated cell mass is called the regeneration blastema. These cells will continue to proliferate, and will eventually redifferentiate to form the new structures of the limb.
        The proliferation of the salamander limb regeneration blastema is dependent on the presence of nerves. Hence statement D is also incorrect.