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[15] [16] [17] In some cases a shed limb can itself regenerate a new individual. [18] Limited regeneration of limbs occurs in most fishes and salamanders, and tail regeneration takes place in larval frogs and toads (but not adults). The whole limb of a salamander or a triton will grow repeatedly after amputation.
A white-headed dwarf gecko with tail lost due to autotomy. Autotomy (from the Greek auto-, "self-" and tome, "severing", αὐτοτομία) or 'self-amputation', is the behaviour whereby an animal sheds or discards an appendage, [1] usually as a self-defense mechanism to elude a predator's grasp or to distract the predator and thereby allow escape.
Salamanders' limb regeneration has long been the focus of interest among scientists. The first extensive cell-level study was by Vincenzo Colucci in 1886. [130] Researchers have been trying to find out the conditions required for the growth of new limbs and hope that such regeneration could be replicated in humans using stem cells.
Similar to other salamanders, P. waltl can regenerate lost limbs, injured heart tissue, lesioned brain cells in addition to other body parts such as the eye lens and the spinal cord. The 20 Gb genome of P. waltl has been sequenced to facilitate research into the genetic basis of this extraordinary regenerative ability.
Some amphibians and certain species of fish and two species of African spiny mice can produce blastemas as adults. [5] For example, salamanders can regenerate many organs after their amputation, including their limbs, tail, retina and intestine. [6] Most animals, however, cannot produce blastemas.
During regeneration, only cartilage cells can form new cartilage tissue, only muscle cells can form new muscle tissue, and so on. The dedifferentiated cells still retain their original specification. [12] To begin the physical formation of a new limb, regeneration occurs in a distal to proximal sequence. [17]
Hox genes play a massive role in some amphibians and reptiles in their ability to regenerate lost limbs, especially HoxA and HoxD genes. [1]If the processes involved in forming new tissue can be reverse-engineered into humans, it may be possible to heal injuries of the spinal cord or brain, repair damaged organs and reduce scarring and fibrosis after surgery.
It revealed species-specific genetic pathways that may be responsible for limb regeneration. [35] Although the axolotl genome is about 10 times as large as the human genome , it encodes a similar number of proteins, namely 23,251 [ 35 ] (the human genome encodes about 20,000 proteins).