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Credit: Igor Schneider

Could a super-fish with regenerative powers help humans regrow lost limbs?

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Sep 20, 2020, 4:59 PM EDT (Updated)

Human limitations are part of the reason we conjured up meta-humans with DNA that enables them to do things we could never dream of doing, such as fly, turn invisible, and regenerate.

The West African lungfish sounds like a creature spawned from science fiction. It can regrow its tail and fins if hungry jaws snap a part of it off, much like a salamander. Its incredible regeneration abilities indicate that these particular traits came from a common vertebrate ancestor — and humans are also vertebrates. Now evolutionary biologist Igor Schneider and his research team are trying to understand the mechanism behind this almost paranormal power, and how it could apply to a human.

Since lungfish are our closest extant fishy relative, it's feasible that a superhero-style breakthrough could eventually come out of this.

“Lungfish relate to us in unique ways, including how their fins (equivalent to our arms and legs) have equivalent bones to the humerus in the arm and the femur in the leg,” Schneider, who recently published a study in Proceedings of the Royal Society B: Biological Sciences, told SYFY WIRE. “They possess true lungs and are obligate air-breathers. They will drown without access to air.”

Regrowing a severed limb doesn’t just happen in a matter of seconds like it does in the movies. Everything that was lost, from muscle to the spinal cord and vertebrate, needs to be replicated cell by cell. Whatever cells are needed migrate to where the limb was bitten off and multiply until the tail fully reappears in a few weeks. Macrophage cells that rush to the wound in an immune response are involved in this process. These cells are responsible for a large part of lungfish and salamander regeneration. They are also found in humans, and while they don’t turn us into The Lizard, they devour pathogens and activate healing by zapping inflammatory and anti-inflammatory signals to the brain.

Though considerable progress has been made in finding out what happens physically when a lost limb is regrown, the genetic mechanisms at work behind limb regeneration are still being demystified. What we really need to figure out is whether the common ancestor we share with the lungfish could also regenerate, and if so, whether the mammalian creatures that would end up evolving into humans either lost this ability as mammals or never invented it. It could be that mammals lost this ability when their ancestors diverged from other vertebrates. Another possibility is that it was never there to begin with but arose in lungfish and salamanders.

The lungfish has an enormous genome, and whether the genes that turn on are critical to regeneration is another question that has yet to be answered. Schneider’s findings suggest there could eventually be a way of rearranging human genes that will give us this superhuman ability.

Yes, we are actaully related to this creature. Credit: Igor Schneider

“What we’ve learned so far is that many of the genes used in regeneration are also used during embryonic development and in other processes in the human body,” he said. “Currently, our findings indicate that our failure to regenerate is not a matter of lacking the right genes, but failures of activating the genes we have in the correct sequence and correct time.”

There is also a signaling gene, SHH, that sends the brain instructions for making a protein called Sonic Hedgehog. This protein is actually named after the spiky blue character that can roll himself into a ball and speed across video game landscapes in a blue blur. The gene signals formation processes in the embryonic stage, which includes cell growth and specialization, body formation, and development of multiple body parts including the spinal cord and limbs.

Some parts of the lungfish regenerative mechanism are already present in humans. Though we look nothing like this bizarre species, its fins and tail have the same muscle, bone, and nerve tissue that are found in our arms and legs. We are also both vertebrates with a spinal cord. The drastic difference is that the lungfish’s spinal cord grows back when it regenerates its tail, but injuries to human spinal cords are often permanent. Unlocking the way that a lungfish regenerates its spinal cord could make irreparable spinal injuries a thing of the past. Future hospitals could have a regeneration wing.

“If we can figure out how they achieve this, we may be able to better understand why humans can’t heal spinal cord injuries and in the future develop strategies to successfully repair this tissue,” said Schneider. “I believe studying regeneration in multiple species will help us discover the key genetic signals required to kickstart regeneration. Once we identify these early signals, we can develop strategies to reactivate these signaling pathways in humans.”

Being related to a weird-looking fish obviously has its advantages.

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