Salamanders can regenerate lost body parts like limbs, tail, eyes, heart and brain. Unlike humans, who can heal only minor wounds, salamanders can completely regrow complex structures, leaving no trace of injury.
Salamanders are amphibians belonging to the order Urodela. The skin of some species has the powerful poison tetrodotoxin. These salamanders tend to be slow-moving and have bright warning coloration.
Their long sinuous bodies are well adapted to different environments. Some aquatic species, such as sirens and amphiumas, have reduced or absent hind limbs, giving an eel-like appearance.
Climbing species have elongated, square-tipped toes. Rock-dwellers tend to have larger feet with short, blunt toes. The regeneration abilities of salamanders inspire self-healing silicone in robotics and other applications.
Healing & Regeneration
1. Wound Closure and Blastema Formation
When a salamander loses a limb, the first step is rapid wound closure. The body stops the bleeding through the process of hemostasis.
Specialized cells rapidly migrate to the site to form a protective layer, preventing infection and initiating the regenerative process. Unlike human wound healing, this closure doesn't involve scar tissue formation.
Next, a mass of undifferentiated cells, known as a blastema, forms at the wound site. These mature cells, derived from various tissues near the amputation, essentially revert back to a stem cell-like state.
They lose their specialized functions. This gives them the potential to develop into any cell type needed to rebuild the missing structure.
2. Proliferation
Once in the blastema, these dedifferentiated cells proliferate rapidly, increasing amount of building matter available for regeneration. Controlled cell division is crucial. Uncontrolled proliferation can cause tumors.
3. Patterning & Tissue Differentiation
With enough regenerative cells, they begin the complex task of rebuilding the lost limb. They re-establish the correct pattern and organization of tissues, a process driven by signaling molecules giving positional cues.
These cues guide the blastema cells to differentiate into the appropriate cell types such as skin, muscle, bone, nerves, blood vessels. Cell types form in correct location and orientation.
During this phase, the new limb takes shape similar to how limbs are formed in embryonic development. Muscles, bones, and nerves organize themselves to regenerate the original structure.
4. Maturation & Functional Integration
In the final stage of regeneration, the new limb matures and integrates with the salamander's body. Blood vessels deliver nutrients and oxygen. The nervous system connects with the new tissues for normal movement.
5. The Immune System
Salamanders have a unique immune response to minimize scarring and promote tissue repair. Specific types of immune cells and signaling molecules suppress inflammation and create new tissue instead of scars.
Specific genes are important to the regeneration process. Salamanders express genes to promote limb regrowth, while these genes are inactive in many other vertebrates.
For instance, the gene regenerating islet-derived protein 1 (Reg1) is needed to form the blastema. Activating similar genes in humans may have medical and cosmetic properties.
The advancement of gene editing techniques like CRISPR could unlock regenerative pathways in human tissues. This research could soon lead to methods for repairing injury damage.
Why Humans Can't Regenerate Like Salamanders
While humans share many of the same genes and cellular pathways as salamanders, the difference is in the way these pathways are regulated.
Human cells don't readily dedifferentiate. Wound healing process often results in scar tissue, and the immune system responds differently to injury.
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