Investigating the Cellular Biochemistry of Spinal Regeneration in Geckos
A broadening collection of research groups are investigating various highly regenerative species - zebrafish, salamanders, spiny mice, and in this case geckos - in order to understand what exactly how they achieve regrowth of lost limbs and organs. The answers will probably be at least slightly different in each case. It remains to be seen as to whether or not the basis for a near-term therapy for human medicine is there to be uncovered, a way to make a comparatively small adjustment to our biochemistry that leads to similar outcomes. Maybe so, maybe not.
Many lizards can detach a portion of their tail to avoid a predator and then regenerate a new one. Unlike in mammals, the lizard tail includes part of the spinal cord. Researchers have found that the spinal cord in the tail contained a large number of stem cells and proteins known to support stem cell growth. "We knew the gecko's spinal cord could regenerate, but we didn't know which cells were playing a key role. Humans are notoriously bad at dealing with spinal cord injuries, so I'm hoping we can use what we learn from geckos to coax human spinal cord injuries into repairing themselves."
Geckos are able to regrow a new tail within 30 days - faster than any other type of lizard. In the wild, they detach their tails when grabbed by a predator. The severed tail continues to wiggle, distracting the predator long enough for the reptile to escape. In the lab, researchers simulate this by pinching the gecko's tail, causing the tail to drop. Once detached, the site of the tail loss begins to repair itself, eventually leading to new tissue formation and a new spinal cord. For this study, the team investigated what happens at the cellular level before and after detachment.
They discovered that the spinal cord houses a special type of stem cell known as the radial glia. These stem cells are normally fairly quiet. "But when the tail comes off, everything temporarily changes. The cells make different proteins and begin proliferating more in response to the injury. Ultimately, they make a brand new spinal cord. Once the injury is healed and the spinal cord is restored, the cells return to a resting state." Humans, on the other hand, respond to a spinal cord injury by making scar tissue rather than new tissue, he added. The scar tissue seals the wound quickly, but sealing the injury prevents regeneration. "It's a quick fix, but in the long term it's a problem. This may play a role in why we have a limited ability to repair our spinal cords. We are missing the key cell types required."