Mapping how the ‘immortal’ hydra regrows cells may demystify regeneration

The tiny invertebrates can regrow their bodies from just a bit of tissue


SELF-RENEWAL  Fluorescent markers reveal which genes are turned on as hydras' stem cells develop into specific cell types. For instance, nerve cells light up magenta in one hydra (second from left).  Another (second from right) shows gene activity behind two of the stages of development (early, green; late, red) of the animal’s stinging cells.

Stefan Siebert and Yashodara Abeykoon/Juliano lab at UC Davis

Hydras seem to have found the fountain of youth, perpetually renewing their cells and regrowing damaged body parts. The tiny tubelike creatures, with a tentacle-ringed mouth and a sticky foot, can regrow their entire bodies from just a scrap of tissue.

These freshwater invertebrates’ regenerative superpowers hinge on three groups of stem cells that develop into specific cells of the hydra’s nerves, glands and other tissues. Scientists now have the best map yet of which genes turn on as stem cells journey toward their fates, researchers report July 26 in Science.

“Most animals have about the same genes,” says Celina Juliano, a developmental biologist at the University of California, Davis. But hydras somehow use that shared genetic toolkit “to do these crazy things,” she says.

Juliano and colleagues analyzed nearly 25,000 individual cells from adult hydra polyps to find which genes were active inside each cell. “Every 20 days, it’s basically a completely new animal,” Juliano says. This constant turnover let researchers track gene activity and catch the steps that stem cells go through as they develop.

The researchers could also watch how specific genes’ activity plays out across an animal’s body, by creating fluorescent probes that find and latch onto RNA in cells. For instance, nerve cells that cluster at the foot and near the tentacles lit up magenta in one hydra. For the hydra’s nervous system, researchers were also able to use the technique to map the development of 12 different types of nerve cells.

Scientists working toward regenerating tissue in humans may have something to learn from these creatures. “If you work with these regenerative organisms, like hydra, you can come up with fundamental principles of how regeneration works,” Juliano says.

hydra tentacles
BODY DOUBLE The roughly 1-centimeter-tall hydra is crowned by tentacles and anchored by a sticky foot. These animals can grow back their bodies from just a bit of tissue and don’t appear to age. Stefan Siebert/Juliano lab at UC Davis

Carolyn Wilke is a freelance science journalist based in Chicago and former staff writer at Science News for Students. She has a Ph.D. in environmental engineering from Northwestern University.

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