Salamanders, Doctor Who and the secret of regeneration

The only special effects here are cells, which have been stained green, wrapped around nerve fibres as the axolotl regenerates a limb.
D.Knapp/E.Tanaka via Nature

By Jess Devonport, Marketing and Communications Officer at the Society of Biology

Matt Smith recently broke the internet by announcing that he would be leaving Doctor Who. This has come as something of a shock to fans, and has led to much debate over who the Eleventh Doctor will regenerate into (for what it’s worth, my vote is for Tilda Swinton).

For the uninitiated, the regeneration of the Doctor is a very handy little plot device that has allowed the show to continue for 50 years despite actors getting bored and leaving. However, aside from some wibbly-wobbly special effects, the show itself has never actually addressed how the Doctor regenerates.

Research published last month by James Godwin and colleagues from the Australian Regenerative Medicine Institute gave new insight into the mechanisms of limb regeneration in salamanders. Now, I realise that salamanders are not Gallifreyan Time Lords, but they do have some pretty neat regeneration skills. Salamanders can regenerate complex body parts such as limbs, tails, retina, and spinal cord, as well as parts of the brain and heart.

Godwin showed that immune cells called macrophages are critical to the early stages of limb regeneration in axolotls, aquatic salamanders. Macrophages are responsible for clearing away dead cells and are involved in inflammation. They have also been shown to be important in scar-free wound healing and tissue and organ development in mammals.

When researchers removed macrophages from the axolotls, they were unable to regrow limbs and instead grew scarred stumps. Once the macrophages had been replenished and the stumps removed the axolotls were able to grow their limbs back, which is nice.

Admittedly, James Godwin wasn’t looking for the answer to the Doctor’s longevity, but he is hopeful that this research could have implications for regenerative medicine.  “We can look to salamanders as the template for what perfect regeneration looks like,” he said. “We need to know what salamanders do and how they do it well, so we can reverse-engineer that into human therapies.”

Growing complete limbs may still be beyond the reach of current medical science, but the study might lead to new treatments for heart and liver diseases, and to prevent harmful scarring following surgery.

With the aid of some sketchy special effects, Matt Smith could possibly regenerate into an axolotl

Regeneration of the Doctor may not be entirely explained by macrophages, but it might be the reason he was able to grow his handy spare hand.

Godwin, J., Pinto, A., & Rosenthal, N. (2013). Macrophages are required for adult salamander limb regeneration Proceedings of the National Academy of Sciences, 110 (23), 9415-9420 DOI: 10.1073/pnas.1300290110