Some species of salamanders have an amazing adaptation known as autotomy. These means that if something or someone snags the tail of this creature, it can make it fall off and regenerate a new one later. Some salamanders have even been able to regenerate legs, parts of their spinal cord, organs, lower jaws, eyes and hearts. At first the new tail or body part when it regenerates may look pale in comparison to the rest of the salamander, but give it some time and eventually the colors will match again perfectly.
If a salamander gets into a fight with a predator it may sacrifice its tail or another part of its body and will regenerate a new one within a few weeks. In fact salamanders are among the highest order of animals that are capable of regererating body parts. This regeneration process involves shuffling around cells at the wound site and assigning them a new specialization.
Within a few hours of losing a body part such as a tail, the salamander’s epidermal cells in the area migrate to cover the open flesh. That layer of cells then gradually thickens in the following days and forms the apical epithelial cap. Cells within the salamander’s tissues called fibroblasts also congregate beneath this epidermal covering. These fibroblasts are undifferentiated which means that they are free to become multiple types of cells depending on which body part the salamander needs to replace.
After this initial phase passes, the blastema develops from the mass of fibroblasts and will eventually become the replacement body part. Interestingly enough researchers recently discovered that the expression of a protein called nAG is what kick starts the blastema growth. This blastema is in turn sort of similar to a mass of human stem cells in that it has the potential to grow into various limbs, organs, and tissues. What is even more astounding is how the salamander knows which body part needs replacing. The genetic coding in the blastema contains a positional memory about the location and type of missing body part. This data is stored in the Hox genes and in the fibroblast cells.
While all of this is busy happening, blood vessels otherwise known as capillaries are regenerating into the blastema. As these blastema cells divide and begin to multiply, the resulting mass becomes a bud of undifferentiated cells. In order for that mound to become a full fledged limb, tail, or what have you, it must receive stimulation from nerves. However, when salamanders drop their tails, they not only lose flesh, they also lose nerves. That means that nerve axon regeneration is also happening at the wound site in tandem with tissue, bone, and muscle regeneration.
It is from there that these cells differentiate and create the appropriate body part that needs to be replaced. As part of the positional memory located in the fibroblast cells, the blastema knows to grow in the proper sequence to avoid defective regeneration. For example, if a salamander loses a foot at its ankle, the blastema will develop outward to form a foot rather than an entire leg.