Scientists have proven what many people probably suspected to be true: regenerating lost limbs is bloody difficult. In fact, it’s so tricky that, even though several non-related creatures are able to do it, it looks as though the ability to regrow body parts may have evolved only once in the history of life on Earth.
Among the many animals capable of regenerating severed appendages are axolotls – also known as Mexican salamanders – zebrafish, and a type of reedfish called bichirs. Though the three creatures are very distantly related, having diverged from a common ancestor around 420 million years ago, the basic mechanism behind their ability to regrow limbs is the same.
The process begins when a body part is lost, such as when it is bitten off by a predator, at which point a type of undifferentiated tissue called blastema begins to develop into the required cells at the site of the wound, until the annexed feature is regrown.
By amputating limbs from all three of these species and then analyzing the genetic material in the cells around the injury, the researchers noted that they all shared 10 common snippets of RNA, or microRNAs. Looking at the genes targeted by these microRNAs, they then discovered that many are in fact highly implicated in the formation of blastema, and therefore probably play a key role in the animals’ regenerative abilities.
For instance, a microRNA called miR-21 was found to be highly upregulated in the wounded tissue of all three creatures, leading to the expression of several genes that enable blastema to develop. As such, reporting their findings in the journal PLOS One, the study authors conclude that the axolotl, zebrafish, and bichir all regenerate limbs using the same genetic mechanism, indicating that they all inherited this ability from a distant common ancestor rather than evolving it independently.
Though there may not be any immediate practical implications for this new knowledge, it does at least tell us that if we were to ever attempt to reprogram humans with the ability to regenerate, the microRNAs found in these three creatures would probably provide the perfect blueprint.