On the Immortality of the Jellyfish
Since time immemorial, humanity has sought ways to cheat death itself. From Sisyphus’ gambit against Thanatos to Gilgamesh’s quest to avoid Enkidu’s fate, from Māui in Polynesia to Houyi in China, the chase for eternal life is a central myth in virtually every culture; and be it ambrosia or mercury, the philosopher’s stone or the apples of Iðunn, items rumored to bestow immortality abound in folklore. Not even the modern world is spared of such myths: Though the heroes of old have been ousted by doctors and scientists, the hope that a miracle cure will be found for the greatest plague of Man remains; and even if immortality in the strict sense is not achievable, the consolation prize of an extended life is more than what anyone could ask for – the more one can stave off the reaper, the better. After all, it is natural to fear the unknown and what awaits mankind beyond the mortal coil is censored better than what occurs within a black hole’s event horizon.
The myriad immortality myths folklore has to offer tend to share a common factor: Those who have already attained eternal life are often nonchalant about the worries of us bumbling mortals. As far as biology is concerned, this couldn’t be truer: Some of the animals closest to immortality happen to be in a mutual pact of ignorance with humans, a pact only broken when an unlucky swimmer steps on one by accident, for those sea-dwelling immortal hermits, known to vernacular as sponges, are not equipped with a means to move out of the way. Representatives of a crucial early step from single-celled life to complex multicellular animals, the basal status of sponges is exactly what grants them their longevity: Their relatively unspecialized tissue is easy to regenerate and they need not to take into account how to replace limbs and sensory organs upon their loss, because they lack such things completely. However, even though long-living sponges can endure for millennia, this is not to say that all sponges can live forever, as an organism can be more successful with a shorter lifespan, e.g. by allocating more resources to reproduction. Death may be an effective survival tactic for a species.
But with great specialization comes great complexity, and with great complexity comes great difficulty when attempting to balance cell senescence (that is to say, aging) with excessive cell proliferation (which equates to cancer) and in the end it’s nigh-impossible for us humans to make use of the sponge’s way of life. Bacteria, the poster children of biological immortality, are likewise not possible to imitate and have already been demonstrated to age in their own way. There is, however, a relatively complex animal with the ability to reverse the clock and revert to its juvenile form, only to mature again and repeat the cycle, potentially ad infinitum. Known mostly by their binomial designations, Turritopsis nutricula and similar hydrozoans are the only known animals with this property and the former has already made a name for itself as the immortal jellyfish, but more important than what it does is how it does it: Normally, bodily cells are derived from stem cells and lack the ability to differentiate any further, but this tiny jellyfish is capable of transdifferentiation, that is to say it can facilitate further modification of a terminally differentiated cell into completely different cell types.
Though the process not difficult to explain, its implications are vast, especially if human cells are capable of undergoing similar transformations. While it might seem unlikely that jellyfish and humans share their molecular machinery to such an extent, even the most basal of animals have a large number of genes with human homologs and similar processes occur in more derived animals such as newts during limb regeneration, and thus the reverse development of Turritopsis may have an equivalent in us. If the molecular mechanism that guides the transdifferentiation process in Turritopsis is indeed applicable to humans, patients waiting for organ transplants will benefit greatly, since this will enable the differentiation of widely available tissue into rarer types. For example, a cardiac patient might be able to “convert” some of his veins into an aortic valve or a patient with corneal ulcer may likewise grow a replacement from his own tissues. In addition, the molecular processes behind the reverse differentiation of the immortal jellyfish might offer insight into the development of stem cells, potentially allowing the generation of iPS cells without the use of oncogenes such as c-Myc and Klf4. Efforts to generate iPS cells without those factors are already underway, and the genome of Turritopsis has the potential to reveal suitable methods.
Even though our pride wouldn’t let us admit it, much of humanity’s so-called modern technology is either found in nature or an explicit imitation thereof. Insect wings are studied to construct small, autonomous flying vehicles, the desert beetle Stenocara collects water from the air in a unique manner that inspired efforts to gather water in arid regions, glass sponges synthesize optical fibers superior to man-made equivalents and myriad other examples of flawlessly optimized natural constructs exist in virtually every branch of science. This is hardly surprising, for nature holds her inventions to standards no engineer can match, where any error is punishable by extinction and constant competition by other designs necessitates constant innovation – it takes all the running a species can do, just to keep in the same place. In Turritopsis, we have an animal that has weathered selective pressures to evolve a system that allows it to cheat death, a system that is perfected over millions of generations. It is only a matter of studying the molecular basis of the hydrozoan’s developmental pathways and seeing what benefit humanity may derive from it. Even if immortality is still a long way away, perhaps, after a long line of errors involving drinking mercury and going on Grail quests, it’ll turn out to be just what we were looking for.
