NIH Record - National Institutes of Health

Squishy Sea Creatures Yield Clues to Aging, Healing

Microscope image of Hydractinia symbiolongicarpus.
Researchers sequenced RNA from Hydractinia symbiolongicarpus, a small, tube-shaped animal that lives on the shells of hermit crabs.


NIH researchers uncovered insights into healing and aging by studying how a tiny sea creature regenerates an entire new body from only its mouth. 

The researchers sequenced RNA from Hydractinia symbiolongicarpus, a small, tube-shaped animal that lives on the shells of hermit crabs. As the Hydractinia were beginning to regenerate new bodies, the researchers detected a molecular signature associated with the biological process of aging, also known as senescence. 

According to the study published in Cell Reports, Hydractinia demonstrate that the fundamental biological processes of healing and aging are intertwined.

Humans have some capacity to regenerate, like healing a broken bone or even regrowing a damaged liver. Some other animals, such as salamanders and zebrafish, can replace entire limbs and replenish a variety of organs. However, animals with simple bodies, like Hydractinia, often have the most extreme regenerative abilities, such as growing a whole new body from a tissue fragment.

A regenerative role for senescence stands in contrast to findings in human cells. 

“Most studies on senescence are related to chronic inflammation, cancer and age-related diseases,” said Dr. Andy Baxevanis, senior scientist at NHGRI and an author of the study. “Typically, in humans, senescent cells stay senescent, and these cells cause chronic inflammation and induce aging in adjacent cells. From animals like Hydractinia, we can learn about how senescence can be beneficial.”

Dr. Andy Baxevanis
Dr. Andy Baxevanis


In humans, stem cells mainly act in development, but highly regenerative organisms like Hydractinia use stem cells throughout their lifetimes. 

Hydractinia stores its regeneration-driving stem cells in the lower trunk of its body. However, when the researchers remove the mouth—a part far from where the stem cells reside—the mouth grows a new body. Unlike human cells, which are locked in their fates, the adult cells of some highly regenerative organisms can revert into stem cells when the organism is wounded. The researchers therefore theorized that Hydractinia must generate new stem cells and searched for molecular signals directing this process.

The researchers scanned the genome of Hydractinia for sequences like those of senescence-related genes in humans. Of the three genes they identified, one was “turned on” in cells near the site where the animal was cut. When the researchers deleted this gene, the animals’ ability to develop senescent cells was blocked and, without the senescent cells, the animals could not regenerate.

We humans last shared an ancestor with Hydractinia—and its close relatives, jellyfish and corals—over 600 million years ago, and these animals don’t age at all. Therefore, the researchers theorize that regeneration may have been the original function of senescence in the first animals.

Drawing of tube-shaped Hydractinia symbiolongicarpus.
Diagram showing the composition of the Hydractinia symbiolongicarpus.

Photo:  Credit Darryl Leja, NHGRI

“We still don’t understand how senescent cells trigger regeneration or how widespread this process is in the animal kingdom,” said Baxevanis. “Fortunately, by studying some of our most distant animal relatives, we can start to unravel some of the secrets of regeneration and aging—secrets that may ultimately advance the field of regenerative medicine and the study of age-related diseases as well.” 

‘Show Us Your BRAINS’ Winners Named

scientific image of brains cells resembling a line of green, yellow, and cream-colored balloons on strings floating in a black background
Winner in the photo category of ‘Show Us Your BRAINS!’ 2023, first place

Winners of the 2023 Show Us Your BRAINS! Photo and Video Contest were announced June 12 by NIH BRAIN Initiative Director Dr. John Ngai. The popular annual contest showcases artistic, eye-catching images and videos of the brain—many using technologies that were developed with initiative support.

Winning photos are:

First Place: “Dark Commute at 4 a.m.” by Silas Busch, University of Chicago. A confocal image of sparse GCaMP6f-expressing Purkinje cells in mouse cerebellum resembles the industrious contours of pre-dawn commuters.

scientific image of the brain with a globe at center with multi-color explosions popping off the top
Winner in the photo category of ‘Show Us Your BRAINS!’ 2023, second place

Second Place: “Premotor Neurons Controlling the Fruit Fly Leg” by Andrew Cook, Jasper Phelps, Anthony Azevedo, Ellen Lesser, Leila Elabbady, Brandon Pratt, Wei-Chung Allen Lee and John Tuthill, University of Washington and Harvard Medical School. Reconstruction of premotor neurons from a serial-section electron microscopy dataset of the Drosophila female adult nerve cord.

Third Place: “Memory Lanes” by Tyler Ard, University of Southern California Stevens Neuroimaging and Informatics Institute. A rendering of MRI data—combining cortical surface and hippocampal segmentations from a T1 weighted scan and diffusion tractography.

scientific image of the brain with white gossamer-like circuitry
Winner in the photo category of ‘Show Us Your BRAINS!’ 2023, third place

Winning videos are:

First Place: “Simian symphony: ripple assembles during rest” by Kari Hoffman, Tyler Sloan and Saman Abbaspoor, Vanderbilt University. Related CA1 unit ensembles from macaque wireless Deep Array recordings, sonified by unit and visualized by layer and functional cell type.

Second Place: “Functional Ultrasound Localization Microscopy” by Alexandre Dizeux, Physics for Medicine Paris. Functional ultrasound localization microscopy reveals whole brain vascular changes during neuronal activation up to the micron scale.

Third Place: “Synaptic Balance” by scalable minds (Germany). Reconstruction of inhibitory and excitatory neurons in human cortex from SBEM.

To view all the images and videos, visit:

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