Turritopsis dohrnii

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Introduction

Figure 1: Turritopsis dohrnii in its mature medusa stage. Photo credits: Takashi Murai, https://www.nytimes.com/2012/12/02/magazine/can-a-jellyfish-unlock-the-secret-of-immortality.html?src=me&ref=general.

Turritopsis dohrnii (previously classified as Turritopsis nutricula),[1] commonly known as the immortal jellyfish or the Benjamin Button jellyfish,[2] is a small species of jellyfish known for its unique ability to revert back to an earlier life stage through transdifferentiation.[3][4] This ontogeny reversal renders the organism virtually immortal as this process has the potential to repeat itself indefinitely, although organismal death does still occur in its natural environment.[5] Reverse development can be triggered by a variety of stressors including starvation, changes in temperature or salinity, physical damage, or age-related deterioration.[4]

Although a rare ability, reverse development has been reported in several other Cnidaria species. Some of these include Laodicea undulata,[6] Aurelia sp.,[7] Hydractinia carnea,[3] Podocoryne carnea, Eleutheria dichotoma, Cladonema sp. and Cladonema uchidai, and Perarella schneideri.[5] However, these species can only undergo reverse development during the early stages of medusa bulb development. What makes Turritopsis dohrnii unique is its ability to revert after sexual maturation.[5]

The immortal nature of Turritopsis dohrnii makes it of interest for research in aging, cancer, and regenerative medicine.








Life Cycle

Figure 2: Life cycle pathways of Turritopsis dohrnii. Photo credits: Yui Matsumoto, https://www.g3journal.org/content/ggg/9/12/4127.full.pdf.
Figure 3: Stages of reverse development in Turritopsis dohrnii. The stage can be grouped into five categories: medusae (Stage 0), reducing (Stages 1-4), stolon (Stages 5-7), polyp bud (Stage 8), and polyp (Stage 9).[3] Photo credits: Stefano Piraino, https://www.researchgate.net/figure/Stages-of-reverse-development-in-Turritopsis-dohrnii-A-Control-medusa-one-day-old_fig3_6617831.

If produced sexually, the life cycle of Turritopsis dohrnii begins with planula larvae, fertilized eggs that settle on the seafloor.[8] From there, it develops into its hydroid stage. In this stage, it now takes on the form of stolons and polyps that reproduce asexually to form a colony. Immature medusae then bud off of the polyps and develop into sexually mature medusae, characterized by the presence of at least 16 tentacles,[9] within 18 to 30 days depending on the temperature of their environment.[5] The mature medusae may then release gametes that form planula larvae if they undergo fertilization, repeating the cycle. However, unlike other species, this is not the only option Turritopsis dohrnii has for restarting the cycle (Figure 2). If faced with unfavorable conditions or physical stresses (such as starvation, changes in temperature or salinity, physical damage, or age-related deterioration)[4] in the immature medusa stage, the organism will skip the maturation and sexual reproductive stages and revert back to the hydroid stage. All mature medusae will spontaneously regress back to the hydroid stage as well, whether or not they face adverse environmental conditions.[5] This reverse development is likely the result of senescence-related stress.

The reverse development process can begin from either the immature or mature medusa stage (Figure 3, Stage 0). The first steps in the process is the reduction of medusa features to create a “ball-like” stage (Figure 3, Stages 1-4), also commonly known as a cyst stage.[3] However, if the organism is in the transitional stage between maturity, characterized by the presence of 13-15 tentacles, there is a 20%-40% chance that the medusa will develop directly into the hydroid stage, skipping the cyst stages.[5] The next step in reverse development is stolon formation in which branches form off the ball-like tissue (Figure 3, Stages 5-7). This step is followed by the formation of a polyp bud (Figure 3,, Stage 8) and finally adult polyp formation (Figure 3, Stage 9).[3] From here, the polyp may asexually reproduce and bud off new medusae. In this sense, Turritopsis dohrnii is “immortal” as it doesn’t die at the end of its lifecycle; it simply starts anew from an earlier developmental life stage.










Genetics and Gene Expression

Figure 4: Phylogenetic tree for Turritopsis dohrnii. Red box highlights Turritopsis dohrnii species. Photo credits: A.A.Lisenkova, https://www.sciencedirect.com/science/article/pii/S1055790316303359?casa_token=zzQIehLx3UwAAAAA:zRnlJmhcU93bxbb4my_kh5LL3z4CLEGjW3WA-aL-UZSl1sa-sQF68dnUdZefETMpK13fAWS5bP8.



Microbial Relationships

Research on the microbiota of Turritopsis dohrnii has not been done, however, there is one interesting microbial relationship that is essential to Hydrozoan development. In order to progress from the planula larvae stage to the hydroid stage, Turritopsis dohrnii require an external signal from marine bacteria.[3] The exact species of bacteria that induces metamorphosis in Turritopsis dohrnii has not been studied, however, there is research on the bacterial inducers for Hydractinia echinta, a closely related Hydrozoan. In Hydractinia echinta, Alteromonas espejiana[10] and other Alteromonas species[11] are known to be strong inducers, but other common marine bacteria, including E. coli can also induce metamorphosis.[11] The presence of these bacterial signals are essential to Hydrozoan development as the planula larvae will not undergo metamorphosis without them.[10]



Medical Potential



Conclusion

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References

  1. ↑ Schuchert P. Revision of the European athecate hydroids and their medusae (Hydrozoa, Cnidaria): families Oceanidae and Pachycordylidae. Revue suisse de Zoologie. 2004 Jun 1;111(2):315-70. Available from: https://www.semanticscholar.org/paper/Revision-of-the-European-athecate-hydroids-and-and-Schuchert/e3d3dce80157e5ee98ecbe0bbe7d35eb36cbe82b?p2df
  2. ↑ Than K. "Immortal" Jellyfish Swarm World's Oceans [Internet]. National Geographic. 2009. Available from: https://www.nationalgeographic.com/animals/2009/01/immortal-jellyfish-swarm-oceans-animals/
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Schmich J, Kraus Y, De Vito D, Graziussi D, Boero F, Piraino S. Induction of reverse development in two marine Hydrozoans. Int J Dev Biol. 2007 Feb 1;51:45–56. Available from: https://www.researchgate.net/publication/6617831_Induction_of_reverse_development_in_two_marine_Hydrozoans
  4. ↑ 4.0 4.1 4.2 Piraino S, De Vito D, Schmich J, Bouillon J, Boero F. Reverse development in Cnidaria. Canadian Journal of Zoology. 2004 Nov 1;82(11):1748-54. Available from: https://www.researchgate.net/profile/Stefano_Piraino/publication/249542511_Reverse_development_in_Cnidaria/links/004635220749d81dc3000000/Reverse-development-in-Cnidaria.pdf
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Piraino S, Boero F, Aeschbach B, Schmid V. Reversing the life cycle: medusae transforming into polyps and cell transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa). The Biological Bulletin. 1996 Jun 1;190(3):302-12. Available from: https://www.journals.uchicago.edu/doi/pdfplus/10.2307/1543022?casa_token=VCv_136r__UAAAAA%3ARVFGUXoAfbOsfuX2x2l8RiTdYNa4mgvDPrnVFQEo5KUbmRat544_LD8iRbOzKJjDNuSi38-gjDo7&
  6. ↑ De Vito D, Piraino S, Schmich J, Bouillon J, Boero F. Evidence of reverse development in Leptomedusae (Cnidaria, Hydrozoa): the case of Laodicea undulata (Forbes and Goodsir 1851). Marine Biology. 2006 May 1;149(2):339-46. Available from: https://link.springer.com/article/10.1007%2Fs00227-005-0182-3
  7. ↑ He J, Zheng L, Zhang W, Lin Y. Life cycle reversal in Aurelia sp. 1 (Cnidaria, Scyphozoa). PloS one. 2015 Dec 21;10(12):e0145314. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4687044/
  8. ↑ Matsumoto Y, Piraino S, Miglietta MP. Transcriptome characterization of reverse development in Turritopsis dohrnii (Hydrozoa, Cnidaria). G3: Genes, Genomes, Genetics. 2019 Dec 1;9(12):4127-38. Available from: https://www.g3journal.org/content/ggg/9/12/4127.full.pdf
  9. ↑ Martell L, Piraino S, Gravili C, Boero F. Life cycle, morphology and medusa ontogenesis of Turritopsis dohrnii (Cnidaria: Hydrozoa). Italian Journal of Zoology. 2016 Jul 2;83(3):390-9. Available from: https://www.tandfonline.com/doi/full/10.1080/11250003.2016.1203034
  10. ↑ 10.0 10.1 Leitz T, Wagner T. The marine bacterium Alteromonas espejiana induces metamorphosis of the hydroid Hydractinia echinata. Marine Biology. 1993 Feb 1;115(2):173-8. Available from: https://link.springer.com/article/10.1007/BF00346332
  11. ↑ 11.0 11.1 Kroiher M, Berking S. On natural metamorphosis inducers of the cnidarians Hydractinia echinata (Hydrozoa) and Aurelia aurita (Scyphozoa). Helgoland Marine Research. 1999 Nov;53(2):118-21. Available from: https://hmr.biomedcentral.com/track/pdf/10.1007/s101520050014.pdf?site=http://hmr.biomedcentral.com


Edited by Bailey Fitzgerald, student of Joan Slonczewski for BIOL 116 Information in Living Systems, 2020, Kenyon College.

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