The Future of Human Healing: Studying Regrowth & Regeneration in the Animal Kingdom
By Amanda Dolan for Scars1
When it comes to healing, the animal kingdom possesses a wide variety of abilities. Humans utilize complex internal healing mechanisms including those related to wound healing, scarring, and skin regeneration. However, there is a significant difference between humans’ healing and the healing of, say, a salamander. If an entire limb of a salamander is cut—it will grow a new one in its place. Some worms, for another example, can even regrow a new head if theirs is severed. The most interesting healing capabilities belong to the flatworm and the sponge who can regenerate every part of their body even if only a tiny portion of them remains. In fact, upon studying healing and regeneration in the animal kingdom, scientists believe that they will better understand how humans heal and how we can improve our own healing abilities.
Some scientists believe that the ability to regenerate is anciently inherent, while other scientists argue that certain organisms have developed these abilities over time through evolution. So important is knowing which of these theories is right, biologist Alexander Bely of the University of Maryland College Park says, “Whether or not regenerative processes are homologous across the animal kingdom profoundly affects how we interpret what we learn about regeneration in different animal groups.”
Until recently scientists looked for a single explanation for the diverse range of regenerative abilities. The singular explanation is that: the more developed and complex a creature becomes over time, the more likely they are to lose the ability to regenerate. Simple organisms, however, evolve less, thereby retaining that ability.
New studies being published in a paper in Trends in Ecology & Evolution takes a deeper look into the genetic makeup of organisms, now attributing the ability to regenerate to multiple factors instead of just one. To see if regeneration comes from a common ancestor, scientists looks to molecular structures in different groups of organisms and consider how physiological and ecological factors should be considered. You can read more about the specific experiments they are performing in this fascinating article from Science News.
Scientists have carefully studied the difference between young and old tissue and the ability to regenerate. One fascinating discovery comes from their work with the flatworm. Though the flatworms they studied were unable to regenerate limbs after being severed, scientists found a way to get them to regenerate. Like other invertebrates, in order for the flatworm to reproduce, they must actively split themselves into two. Scientists found that, if a certain flatworm is severed during this asexual reproductive process, they can actually grow a new head. So, by cutting into a worm during its most active, youthful state, scientists have created regeneration where there otherwise was none.
The scientists think that they were able to do this because younger tissue is able to support regeneration better than older tissue. In fact, this same idea has occurred with humans as well. For example, there have been several reports of young children regenerating fingertips that were severed. Some pediatric surgeons who have administered fetal surgery in early pregnancy found that, later, when the baby was born, he or she was perfectly healed from the surgery without any scars. Some scientists believe that, like other animals, humans possess the ability to heal wounds without scarring and maybe even regrow tissue and limbs. However, this ability lays dormant and inactive because evolution favored patching wounds through scarring instead of regenerating body parts. Bely and her colleagues are studying the flatworm to see exactly how regeneration can be coaxed out of its dormant state into action. The results of these studies may one day allow for the modification of regenerative abilities in humans.
Even more interesting, perhaps, is a study on planarians—a worm that regrows no matter how many pieces it is sliced into. After cloning and testing thousands of planarian genes, scientists found that the majority of the genes used to regenerate are shared by many other types of life forms—including humans. Scientists in the past assumed these certain genes were lost over time, which caused animals to become incapable of regenerating in response to amputation or injury. Now scientists see this is not true. The genes, in fact, are likely still there just being used in slightly different ways.
The group of scientists focusing on these genes are using a process called RNA interference to turn off genes one at-a-time to see how a series of molecular events occur within a cell that allows for both embryonic development and regeneration. They are looking for molecular events like those that signal for a worm to “know” whether to regrow a head or a tail. Their studies, published in Science, show how the two processes involved in embryo development work together, yet still differ—similar to the way events signal regeneration. Identifying molecular events within cells during embryogenesis would be a big step toward learning how humans could possibly access these development “tools” later in life for regeneration and more advance self-healing. This will be a difficult challenge for scientists because the processes of embryogenesis and regeneration same similar qualities but are not exactly alike. One of the biggest differences between how an embryo forms and how a body part regenerates is in the chronology of the task. Embryogenesis moves forward, creating brand new pieces, while regeneration must recreate something that formed years before, during early development. Though these studies are complicated, learning exactly how tissues ‘’know” what to do and understanding how new tissue integrate with old tissue during healing could offer significant clues.
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