What truly makes this little critter unique?

Now that you have a little background on T. nutricula, it is time to discuss the way that they are biologically immortal.

The way that T. nutricula is able to live forever is through a process call transdifferentiation. This process is where normal, adult cells revert to a pluripotent state. Pluripotent means that the cells have the potential to divide into a variety of different cell types. T. nutricula is able to undergo normal, sexual reproduction as well. This is diagramed below under the "Normal" life cycle. However, when environmental pressures increase T. nutricula can revert to a colonial, asexual state. This helps them survive by reducing metabolic requirements, and allowing for formation of a colonial stolon, that in-turn produces a polyp. During this process, T. nutricula can encyst. As a cyst, T. nutricula can stay dormant for extended periods of time until the environmental conditions are favorable. In the form of a polyp, budding can occur that allows for production of more T. nutricula medusa. In most jellyfish, once adulthood is reached, asexual reproduction is no longer possible. T. nutricula always has two options; sexual or asexual reproduction. If there are enough sexually mature, con-specifics around T. nutricula will be able to reproduce sexually. However, if the population density is too low, T. nutricula can just revert to a polyp and reproduce asexually. This asexual route is what makes T. nutricula biologically immortal. It can make exact genetic copies of itself, which means that it is possible for an individual T. nutricula to never die by making clones of itself.

Normal Cnidarian Life Cycle

T. nutricula Extra Life Cycle

Piraino et. al. 1996

What cells are involved in the transdifferentiation process?

In a study by Piraino et. al., different parts of the T. nutricula medusa were isolated and stimulated to undergo transdifferentiation. They found that not every part of the medusa could transdifferentiate. What they found was that just the presence of stem cells (cells that are known to be able to transdifferentiate), is not sufficient to form a stolon. This was shown by the fact that just the manubrium, which does contain stem cells, was not able to form a stolon. They found that what was necessary was the exumbrella as well as cells from the gastrovascular system. If these cell types were present they could transdifferentiate and form a stolon. They also found that striated muscle cells may also contribute to some of the transdifferentiation process.

Their study did not look at the genes required to initiate the transdifferentiation process. Further research is needed to better understand what genes are involved and if these genes can be found in other species.

General Structure of T. nutricula

Piraino et. al. 1996

Sections Isolated in Piraino et. al. Study

Piraino et. al. 1996

The boxes above show the different regions that were isolated, and stimulated to see if they could undergo transdifferentiation. 

Full Results of the Piraino et. al. Study

Piraino et. al. 1996

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2. Carla E, Pagliara P, Piraino S, Boero F, Dini L. Morphological and ultrastructural analysis of Turritopsis nutricula during life cycle reversal. Tissue and Cell [Internet]. 2003 [cited 2013 May 1]. Available from: http://www.sciencedirect.com/science/article/pii/S0040816603000284

8. Miglietta M, Piraino S, Kubota S, Schuchert P. Species in the genus Turritopsis (Cnidaria, Hydrozoa): a molecular evaluation. Journal of Zoological Systematics and Evolutionary Research [Internet]. 2007 February [cited 2013 March 26];45(1):11–19. Available from: http://doi.wiley.com/10.1111/j.1439-0469.2006.00379.x

9. Piraino S, Boero F, Aeschbach B, Schmid V. Reversing the life cycle: medusae transforming into polyps and cell transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa). Biological Bulletin [Internet]. 1996 [cited 2013 April 28];190(3):302–312. Available from: http://www.jstor.org/stable/10.2307/1543022