You may have heard the urban legend that you can cut a worm in two and both halves will live. I thought it was bollocks until I learnt about a special group of worms known as planarians. Their ability to regenerate from injury has been known for quite some time (although not as well-known as Wolverine from X-Men) and scientists are now investigating how they do it in an attempt to find out if they are potentially immortal.
The research group from England used a species of planarian called Schmidtea mediterranea, a freshwater planarian from southern Europe. There are two forms which exist; one which reproduces by having sex and the other which reproduces without sex by splitting itself in half. Both forms have regenerative powers due to a large supply of stem cells.
Our bodies are made up of cells, most of which are specialised to perform a certain job in a certain place. Stem cells are not specialised, but have the ability to divide many times (a process called mitosis) and then differentiate to become any type of cell that the body requires. Humans have a limited number of these cells but planarians have many stem cells spread throughout their body. This gives them fantastic regeneration abilities, allowing both halves of a cut worm to grow back its missing body parts. But this isn’t the only trick Schmidtea mediterranea uses to ward off aging.
Aging is essentially caused by cells becoming unable to multiply and replace old tissue with new. Before a cell divides it has to make a copy of its DNA, one for each new cell. But the copying process involves small sections being cut off the end of the DNA strands, called chromosomes. So that important information isn’t lost, the end of each chromosome has a telomere, a sequence of DNA that doesn’t contain important information and can be cut off without damaging the chromosome. As we age, this telomere gets shorter until it can no longer protect the DNA. When this happens, the cell stops multiplying and the effects of aging start to be seen.
While human stem cells can go through many divisions, eventually their telomeres will become too short to continue dividing. The telomeres can be built back up by an enzyme called telomerase, a discovery of which earned the 2009 Nobel Prize for medicine. Telomerase acts to extend the life of cells which need to multiply regularly but in humans it is mostly active in our early development.
Asexual planarian worms, however, produce large quantities of telomerase when they are regenerating, either from a natural division or being sliced by a scientist. This allows to them to maintain their telomeres at a constant length and prevent aging. While we can’t watch an individual worm forever to see if it stays alive, this finding gives us strong evidence that immortality may be possible for these worms.
Now if only we could give them retractable adamantium claws…
Tan, T. C. J., Rahman, R., Jaber-Hijazi, F., Felix, D. A., Chen, C., Louis, E. J., et al. (2012). Telomere maintenance and telomerase activity are differentially regulated in asexual and sexual worms. Proceedings of the National Academy of Sciences, 109(11), 4209-4214. doi:10.1073/pnas.1118885109.
For more information, watch the video of one of the researchers, Aziz Aboobaker, explaining the research.