Aeschbach, B., Boero, F., Piraino, S., and Schmid, V. 1996. Reversing the life cycle: medusae transforming into polyps and cell transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa). Biological Bulletin 190: 302-312.

Turritopsis nutricula is the only known metazoan that can revert from its adult stage back into a juvenile. What are the triggers that cause the reverse aging process and is it possible to observe it in a laboratory? Has T. nutricula achieved biological immortality?

Some other species of hydrozoans are able to convert from their medusa stage into a polyp stage, but T. nutricula is the only species that can do so after it has reached sexual maturity. T. nutricula have been observed to revert back to their polyp stage under periods of environmental stress. The distinction between medusa and polyps is not only their structural form; they have a different set of somatic cells in their umbrella. RNA fingerprinting has also confirmed a difference in protein expression and therefore T. nutricula is required to transform at the cellular level.

Approximately 4000 T. nutricula medusae were taken from the Mediterranean Sea and after they had reached sexual maturity they were placed in groups of ten. The researches then either deprived the medusae of food or rapidly changed the water temperature. Every medusa subjected to these conditions transformed into a polyp but the medusae not placed under stress did not transform.

Since all T. nutricula were able to transform the researches concluded that this species has found a way to avoid organismic death. The study cannot determine if this process occurs in the wild but it is highly probable that it does.

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(posted Dec. 22 2010)