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Scientists Got Adult Frogs to Regrow Limbs. It's a Step Toward Human 'Regeneration'
Millions of people live with amputated limbs that are gone forever. But that might not be the case in the future. For the first time, scientists have shown that adult frogs can regrow amputated legs. They say the approach can work in humans, too. "There is no reason that human bodies can't regenerate," said Tufts University biologist Michael Levin, who led the new research. "This is the first proof-of-principle of a roadmap for regenerative therapy in human medicine, well beyond limbs," he added. "Many problems — from birth defects to traumatic injury, aging and even cancer — could be solved if we understood how to induce organs to regrow in place."
Ultimately, that's what Levin and his research team at Tufts University in Medford, Massachusetts, want to figure out: how cells cooperate to build a complex three-dimensional organ and "stop exactly when it's done." But first, the scientists needed to try to reproduce organ growth in animals that don't regenerate. Adult African clawed frogs, a common laboratory animal known in scientific circles Xenopus laevis, fit the bill. The amphibians are not normally regenerative but have some tissue renewal capacity, just like humans. "We were hoping to show that adult Xenopus frogs are capable of limb regeneration, and to find a trigger that allows it to happen," Levin said.
The trigger the team found is progesterone, the sex hormone involved in the female menstrual cycle, pregnancy and breastfeeding. The scientists applied the compound to frogs' amputated back legs with a wearable bioreactor device for 24 hours. Then they watched as the limb regenerated.
See also: These Flatworms Can Regrow A Body From A Fragment. How Do They Do It And Could We?
Brief Local Application of Progesterone via a Wearable Bioreactor Induces Long-Term Regenerative Response in Adult Xenopus Hindlimb (open, DOI: 10.1016/j.celrep.2018.10.010) (DX)
(Score: 2) by Immerman on Friday November 09 2018, @03:44PM
Well, it does look like it regrew a great deal more bone, blood vessels and (presumably) muscle, and possibly even the beginnings of a knee and toes - in fact it very much resembles the middle stages of full-limb regeneration in species that can do that. In contrast the control "spike" appears to be almost completely soft tissue, and thus rather useless - probably wouldn't even work as a functional tentacle since the musculature is all designed to work against a skeletal system. Regrowing even a bony muscular stump could mean the difference between a prosthetic leg starting at the knee, or just at the ankle. Though that's probably primarily a psychological difference.
If that's actually the beginnings of a joint though? That could mean the difference between a prosthetic elbow and a real one, and hints at the possibility of regrowing further joints as well, perhaps even the entire limb. If you had the choice between a prosthetic arm starting mid-bicep, or a full natural (if malformed) arm and hand, that could be very tempting. Especially since traditional plastic surgery could reconstruct much of the malformation. Heck, even if all you could regrow properly is a bunch of malformed muscle, bone, and nerve that could open the door to only needing a prosthetic skeleton rather than the full limb. Maybe not an end-goal, but a huge leap forward from where we are today.
And even if all they they can get is mostly non-functional malformed growth that's a *huge* leap forward - essentially they've found a "gas pedal" for the regeneration process. A "steering wheel" is also important for getting where you want to go, but you need to start moving before you can begin experimenting to try to find that.
Oh, and as for that important reason we don't regenerate, we've already found one big one - scarring. In general the more capable an animal is of regenerating, the less scar tissue it forms - and scar tissue appears to serve an important protective function in the immediate aftermath of a wound, especially on land where a fast, durable patch helps seal the wound against fluid loss and further damage. Unfortunately it also interferes severely with further regeneration, but if it keeps you alive long enough to bemoan your loss, then that's a huge win for evolution. Suppress the formation of scar tissue, and even mammals will regenerate a fair bit more than normal. Suppress it *and* stimulate regrowth? We shall see.