The mythical hydra may be capable of regrowing its multiple heads every time it is cut, but there are actual creatures capable of regenerating parts of their bodies that have been severed by hungry predators. Jellyfish are one of them.
The Regeneration Process in Jellyfish
The regeneration process in jellyfish is quite similar to that of amphibians and other animals. All animals capable of regeneration start the repair process by forming a blastema. This mass of proliferating cells, similar to stem cells, can refill body parts by dividing repeatedly. Initially, the cells are undifferentiated, but eventually, specific types of cells such as muscle and skin form.
Blastema Formation in Jellyfish
The process of blastema formation has been studied in some other animals, but how it forms in jellyfish has remained a mystery until now. A research team led by researcher Susuki Fujita from the University of Tokyo and Tohoku University in Japan aimed to establish a foundation for the non-bilateral regeneration process by understanding how blastema aids in regrowing arms in jellyfish. Would their blastema formation process be different from that in bilateral organisms?
“In particular, the current understanding of the blastema formation process relies heavily on bilateral models, and thus the mechanisms of blastema formation outside of bilateral organisms remain poorly understood,” the researchers stated in a study recently published in the journal PLOS Biology.
The Regeneration Process in Jellyfish
The regeneration process in jellyfish has been puzzling. Finally, the Japanese team gained new insights into this process in the jellyfish Cladonema pacificum. They found that the proliferating cells forming the blastema appear only at the sites of injury – they are not the same local stem cells found at the base of the arms. However, both types of cells work together to repair and regrow the severed arms.
Jellyfish are animals belonging to the phylum Cnidaria, a group of invertebrates with soft bodies. Cnidarians also include corals, hydra, and anemones, all of which have smooth arms. Unlike bilateral organisms such as amphibians (and humans), which exhibit bilateral symmetry (meaning there are identical left and right sides), cnidarians have radial body symmetry, with body parts extending from a center and being symmetrical from all sides. They do not have a right side and left side or front and back.
The Regeneration Process in Jellyfish
As jellyfish rely on their arms to catch and immobilize prey, they need to regrow lost arms as quickly as possible. When arms are severed from the Cladonema jellyfish, with the remaining base in place, the wound at the cut site heals completely within just 24 hours. Blastema forms immediately after healing; then new arms begin to grow.
As new arms grow, the number of nematocyst cells, or stinging cells, increases. This indicates that the regeneration process occurs regardless of whether the jellyfish has recently eaten, as its body automatically prioritizes the regrowth of arms to catch food.
When the blastema forms, most of the cell proliferation occurs towards the regenerating tip of the new arms. Three types of differentiated cells were later found in the blastema. These are epithelial cells, which form the inner layers of the arms; i cells, which help jellyfish sense and handle food; and stinging cells. The undifferentiated cells showed a tendency to transform into epithelial cells, as those are the most common cells in fully developed arms.
Most
The cells that form the blastema are not stem cells from the base that migrate to the tip. However, stem cells at the base still have a role to play. The team believes these cells help in the growth of the new arms formed from the base, adding some length while the proliferating cells at the tip elongate. Removing the stem cells at the base would also delay blastema formation by a week or two.
Overall, the process of blastema formation in jellyfish has been shown to be very similar to that observed in bilaterally symmetrical organisms that can regenerate. However, it is still unclear exactly how and where the proliferating cells arise. Researchers believe it is possible that these cells are derived from already differentiated cells that lose their differentiation in order to form the blastema. Examples of poorly differentiated cells forming a blastema have been seen in starfish and lobsters.
Can humans be capable of regeneration?
It might happen. Some experiments on animals that do not normally regenerate have successfully regrown tissues. As the mechanisms behind this phenomenon are better understood, human treatments utilizing regenerative processes may be developed in the future, but for now, this remains in the realm of science fiction.
References: PLOS Biology, 2023. DOI: 10.1371/journal.pbio.3002435
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Elizabeth Rayne: Elizabeth Rayne is a being who writes. Her work has appeared on SYFY WIRE, Space.com, Live Science, Grunge, Den of Geek, and Forbidden Futures. She lurks outside New York City with her parrot, Lestat. When not writing, she is either shapeshifting, painting, or dressing up as a character no one has ever heard of. Follow her on Threads and Instagram @quothravenrayne.
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