Nov. 5, 2021 — Scientists have used gene editing on lizard embryonic stem cells to help adult lizards regrow severed tails, making them the closest species to humans to regenerate a lost appendage.

Lizards have a reputation for dropping their tails in self-defense when attacked, distracting predators long enough to make an escape. The lizards may live to fight another day, but the new tail they grow isn’t quite the same as the old one. It’s a cartilage tube without a spinal column and the nerves needed for most movements.

Now, researchers have used gene-edited stem cells for tail replacement in an all-female species of gecko, coaxing them to generate new tails with nerves and bones, according to findings published in Nature Communications.

During original tail development, researchers found, specific embryonic stem cells drive production of a complete tail, using different signals to promote cartilage growth along the bottom but bone and nerve tissue along the top of the tail.

For a tail replacement, though, adult versions of these stem cells actively signal to block bone and nerve formation and encourage cartilage development only. The result is a cartilage-heavy appendage with limited movement.

When researchers blocked these adult stem cell signals, the lizards still didn’t regrow a complete tail. Implanting the embryonic stem cells into adult tail stubs also had no effect. Bone and nerve tissue development was still blocked.

The scientists weren’t completely stumped, though. They turned to gene-editing tools, crafting embryonic cells that couldn’t respond to signals to block bone and nerve tissue growth. With these edited cells implanted, the lizards regrew tails with bones, nerves and cartilage.

It’s far from certain that this approach could lead to appendage regrowth in other species, including humans. But it does show how understanding these early processes in development can add to the repair toolkit for adults.