Fleets of tiny translucent umbrellas, each about the size of a lentil, waft through the waters of the Mediterranean Sea. These miniature jellyfish are known as Turritopsis dohrnii.
But they have a secret: When their bodies are damaged, the mature adults, known as medusas, can turn back the clock. They shed their limbs, become a drifting blob and morph into polyps, twiggy growths that attach to rocks or plants. Gradually, the medusa buds off the polyp once again, rejuvenated. A predator or an injury can kill T. dohrnii, but they are, effectively, immortal.
In a paper published this month, scientists have taken a look at the jellyfish’s genome, searching for the genes that control this remarkable process.
Gathering enough T. dohrnii to study their genomes can be difficult.
When it comes to living in an aquarium, “they are very picky,” said Maria Pascual-Torner, a scientist at Universidad de Oviedo in Spain.
To boost research, Pascual-Torner and a colleague gathered wild jellyfish in Italy.
They and colleagues noticed the jellyfish had extra copies of certain genes, a sign these might be important for survival. The researchers found many of the duplicated genes among them, including some that protect and repair the jellyfish’s DNA.
To trigger rejuvenation, the researchers put the jellyfish under stress. As the medusas shrank, sprouted polyps and began remaking their adult bodies, the scientists took snapshots of the genes used in each development phase. They took jellyfish in each phase and extracted their mRNA, showing which genes were used to make proteins.
As the jellyfish transformed, the scientists were interested to see a marked change in the use of genes linked to DNA storage. In adults, these genes were active or expressed at a high level. But as the animals began their descent back into polyps, the genes became quieter.
Genes related to pluripotency, or a cell’s ability to grow into fully developed forms, did the opposite. They were quiet in the adult form but leaped into action as a jellyfish broke its body down and started to build it back. The pluripotency genes returned to dormancy when the process was complete.
What this suggests, Pascual-Torner said, is that DNA is brought out during the transformation, and genes that coax cells to reset go into overdrive. — VERONIQUE GREENWOOD / NYT