How jellyfish regenerate their functional tentacles in just a few days

About the size of a pinky fingernail, the jellyfish species Cladonema can regenerate an amputated tentacle in two to three days, but how? Functional tissue regeneration in all species, including salamanders and insects, relies on the ability to form a blastema, a cluster of undifferentiated cells capable of repairing damage and growing to form the missing appendix.

Jellyfish, along with other cnidarians such as corals and sea anemones, exhibit great regenerative abilities, but how they form the critical blastema remains a mystery until now.

A research team based in Japan has revealed that proliferative rod-like cells, which actively grow and divide but do not yet differentiate into specific cell types, appear at the injury site and help form the blastema.

The results were published in Biology PLOS.

“It is important to note that these proliferative stem-like cells in the blastema are different from the resident stem cells located in the tentacle,” said corresponding author Yuichiro Nakajima, lecturer at the Graduate School of Pharmaceutical Sciences at the University of Tokyo. “Repair-specific proliferative cells contribute primarily to the epithelium, the thin outer layer, of the newly formed tentacle.”

According to Nakajima, resident stem cells that exist in and near the tentacle are responsible for generating all cell lineages during homeostasis and regeneration, meaning they maintain and repair all necessary cells during life of the jellyfish. Repair-specific proliferative cells only appear at the time of injury.

“Together, resident stem cells and repair-specific proliferative cells enable rapid regeneration of the functional tentacle within days,” Nakajima said, noting that jellyfish use their tentacles for hunting and feeding.

According to first author Sosuke Fujita, a postdoctoral researcher in the same lab as Nakajima at the Graduate School of Pharmaceutical Sciences, this discovery explains how researchers understand how blastema formation differs among different groups of animals.

“In this study, our goal was to address the mechanism of blastema formation, using the tentacle of the cnidarian jellyfish Cladonema as a regenerative model in non-bilaterians, or in animals that do not form bilaterally – or left-handedly – right – during embryonic development.” Fujita said, explaining that the work can provide insight from an evolutionary perspective.

Salamanders, for example, are bilaterian animals capable of regenerating their limbs. Their limbs contain stem cells restricted to specific cell type requirements, a process that appears to work similarly to the repair-specific proliferative cells seen in jellyfish.

“Since repair-specific proliferative cells are analogous to the limb-restricted stem cells of bilateral salamanders, we can assume that blastema formation by repair-specific proliferative cells is a common, independently acquired feature for complex d-regeneration. “organs and appendages during animal evolution”, Fujita said.

The cellular origins of the repair-specific proliferative cells observed in the blastema remain unclear, however, and researchers say that the tools currently available to investigate the origins are too limited to elucidate the source of these cells or to identify other cells resembling to stems. cells.

“It would be essential to introduce genetic tools allowing the tracing of specific cell lines and manipulation of Cladonema,” Nakajima said. “Ultimately, understanding the mechanisms of blastema formation in regenerative animals, including jellyfish, could help us identify the cellular and molecular components that enhance our own regenerative abilities.”