Jellyfish regenerate lost tentacles, and now we know how to do it

The mythical Hydra may have been able to grow one of its many heads back every time it was decapitated, but there are actual creatures capable of regenerating parts of their bodies bitten off by hungry predators. Jellyfish is one of them.

From salamanders to starfish to actual hydras (a small hydrozoan named after the fearsome mythical beast), all animals capable of regeneration begin the repair process through blastema formation. This group of proliferating cells, which resemble stem cells, can repopulate body parts by dividing over and over again. While the cells are initially still undifferentiated, they eventually form specific cell types such as muscle and skin.

The process of blastema formation has been studied in some other animals, but how it forms in jellyfish remains a mystery. Led by postdoctoral researcher Sousuke Fujita, the team from the University of Tokyo and Tohoku University in Japan wanted to establish a baseline for non-binary regeneration by discovering how the blastema helps regrow jellyfish tentacles. Would the process of blastema formation be different from that in bisexuals?

“In particular, the current understanding of blastema formation is largely based on binary models, and thus the mechanisms of extra-blastema formation remain poorly understood,” the researchers said in a published paper. Stady It was recently published in PLOS Biology.

The regeneration process in jellyfish has been a mystery. The Japanese team finally has a new view of this process in jellyfish Cladonema pacificum. They found that the proliferating cells that form the blastema appear only in the presence of injury, and are not the same as the in situ stem cells found at the base of the tentacles. But both types of cells work together to repair and regrow severed tentacles.

An arm and a leg

Jellyfish are cnidarians, a phylum of soft-bodied invertebrates. Cnidarians They also include corals, hydras, and anemones, all of which have stinging tentacles. Unlike bilateral organisms such as salamanders (and humans), which have bilateral symmetry (i.e. symmetrical right and left sides), cnidarians have radial body symmetry, with body sections extending from the middle and being symmetrical throughout. They have no right, left, front, or back.

Because jellyfish rely on their tentacles to capture and immobilize prey, they need lost tentacles to grow back as quickly as possible. When the claws of Cladonema If it is cut leaving the base or bulb in place, the wound at the site of the cut heals completely in less than 24 hours. Blasts formed immediately after healing; Then new tentacles began to grow.

The more they grow, the more filamentous cells, or stinging cells, there are. This suggested to Fujita and his team that the regeneration process occurs regardless of whether the jellyfish has eaten recently or not, because its body automatically prioritizes regrowing its tentacles to capture food.

They keep growing

When the blastema forms, most of the cell proliferation occurs toward the regenerating tip of the new tentacle. Three types of differentiated cells were later found in the blastema. These are the epithelial cells that form the inner layers of the tentacle. i cells, which help the jellyfish sense and handle food; The filamentous cells are stinging. Undifferentiated cells showed a tendency to transform into epithelial cells because these are the most common cells in fully developed tentacles.

Most of the cells that form the blastema are not stem cells from the bulb that migrate to the tip. But there is still something for onion stem cells to do. The team believes the cells help the newly formed tentacle grow outward from the base, adding some length while proliferating cells elongate it from the tip. Removing stem cells at the base may also delay blastema formation by a week or two.

In general, blastema formation in jellyfish has been shown to be very similar to what is seen in regenerative decapitated helminths. However, it is still unclear how and where reproductive cells arise. The researchers believe that it is possible that these cells are derived from already differentiated cells that differentiate in order to form the blastema. Examples of undifferentiated cells forming the blastema have been seen in starfish and cockroaches.

Could humans be able to regenerate? might happen. Some experiments in animals that do not naturally regenerate have been successful in stimulating tissue regrowth. As the mechanisms behind this phenomenon are better understood, human treatments using regenerative processes may one day be developed, but for now, this remains in the realm of science fiction.

PLOS Biology, 2023. DOI: 10.1371/journal.pbio.3002435