According to a new study published in Proceedings of the National Academy of Sciences, differences in spinal-cord stem cells between salamanders and lizards cause dramatic differences in regenerative abilities. When a salamander regrows it's tail, the new appendage has bone and nerve cells, just like the original, whereas a lizard regrows a tail that is only filled with cartilage, and lacks function.  

Thomas Lozito is a biologist at the University of Pittsburgh, and one of the study's authors. Along with his colleagues, he compared cells from the axolotl salamander to the green anole and the mourning gecko, both species of lizard. According to Lozito, neural stem cells in the salamander spinal cord are able to regenerate into any kind of nervous system cell, whereas lizards have lost this ability over evolutionary time.

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Fluorescence microscopy cross sections of original lizard and salamander tails (on the left) show cartilage as green and nerve cells as red. Regenerated tails on the right show lizard tails of cartilage, while the salamander has developed new nerve cells.

The scientists wondered if the issue was in the lizard cells themselves, or whether there was an environmental cause to the lack of complete regeneration. By implanting salamander neural stem cells into gecko tail stumps, they found that neurons were sometimes formed, which points to the lizard cells themselves being the culprit. They hope to find a way to alter the lizards cells to mimic the regenerative properties that have been lost.A lizard is considered to be more complex from a biological and evolutionary standpoint. More complex species are generally much less capable of regeneration than  simpler species, but the reason for this loss is unclear.

To answer these questions, Lozito and colleagues want to try gene editing using CRISPR/Cas9 in hopes that lizard neural stem cells can be favorably altered. The group also hopes to one day be able to alter mammalian stem cells in order to regenerate limbs and other body parts. As reported in Science News, Lozito declared that their "goal is to make the first mouse that can regenerate its tail.” 

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A lofty goal to be sure, yet the scientists are several decades to late! Dr. Robert Becker already did this very thing, regrowing mouse tails and frog legs in the 80's, as is described in detail in his incredible book, "The Body Electric." He and his team found the unique electrical pulses that when properly timed in an evolving rhythm throughout the period of healing, can stimulate stem cells to differentiate into any cell in the animal. They found these unique pulses by first studying salamanders and later applying the findings to other animals. Why his revolutionary findings have been and still are ignored is a subject for another article. While I find the modern study interesting, it is infuriating to me how these scientists can pretend this is new research.