Hydra DNA Reveals Multiple Ways to Regrow a Head


A tube-shaped carnivore lives in rivers and streams around the world. It paralyzes and captures its prey with a crown of tentacles, then pulls it in through its mouth (which also serves as its anus). This disturbing creature is a hydra, a freshwater cnidarian not more than one half inch tall, eating mainly insect larvae and crustaceans. A hydra’s looks and eating habits alone give it a sci-fi feel, but its ability to reconstruct its body—even its head—from just a clump of tissue or cells elevates it to another level.

“It’s one of those organisms that is thought to never die unless they try to kill it or starve.” Ali Mortazavi“Irvine is a developmental biologist at the University of California,” he said. A hydra’s regenerative abilities allow it to constantly replace parts of itself, so it won’t succumb to things like old age or illness. Along with the immortality advantage, constant regeneration means a hydra doesn’t have to sweat the little things like losing body parts. give a several days and magnifies everything back.

Dr. Mortazavi and colleagues have taken a big step forward in understanding how a hydra regenerates its head. Their research has been published Genome Biology and Evolution Wednesday.

To explore what made this remarkable feat possible, the researchers looked at changes in gene expression (whether a gene is copied from DNA to RNA) during hydra head regeneration. This control of gene expression is called epigenetic regulation. Hydras have a genome quite similar that of species with low regeneration capacity, like people, so epigenetic regulation is thought to play an important role in enabling the regenerative powers of the hydra.

The team discovered dynamic changes in the regulation of DNA stretches, called enhancers. Enhancers increase the likelihood that a gene of interest will be copied from DNA to RNA. The team found that these enhancers help ensure expression of many genes, including those long known to be important for regeneration. Noting that the study put the hydra in the same club as many other animals, including mammals, Dr. “No one knew that the Hira had these empowering areas,” Mortazavi said.

The researchers then compared gene expression during head regeneration with gene expression during budding; hydra grows a polyp it is basically a copy of itself. This process requires a second head to grow, but the researchers found that a budding head forms very differently from a head that regrows after injury.

“When I look at trends in gene expression, the genes increase slowly throughout budding head development, but we noticed these sharp turns in regeneration,” said Aide Macias-Muñoz, a developmental biologist at the University of England. Santa Barbara, California, one of the study authors. “Many genes are turned on, then turned off, and then turned on again. So while the result is the same, the trend actually looks very different.”

Dr. Mortazavi was also surprised to find that the timing of gene expression varied so much between head regeneration and budding. “Obviously there’s more than one way to get high,” he said.

The discovery of these strengthener regions and their role in hydra head regeneration suggest that the evolution of enhancers preceded the evolutionary divergence of the surrounding cnidarians and bilaterians (animals with bilateral symmetry such as humans). 750 million years ago. Erin DaviesA developmental biologist at the National Cancer Institute who studies regeneration but was not involved in the study, Dr.

“They’re really well placed to answer a lot of fundamental questions in developmental biology,” he said. “How did nervous systems evolve? How did you get the binary symmetry?”

Dr. Davies said that such studies are also necessary for the field of regenerative medicine. to restore common purpose diseased and injured tissues and even entire organs.

“If you have a good grasp of a paradigm in any animal system,” he said, “then you can start to think about how you can turn things around in species that are less capable of regeneration, such as mammals.”



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