In ancient Greek mythology, Hercules fought the multi-headed, snake-like hydra. Although Hercules ultimately prevailed, the battle seemed hopeless at first. Each time one of the beasts’ heads was severed, two heads would replace the lost one. Recently, reality become eerily similar to the myth of the hydra when a regenerating planarian flatworm (D. japonica) sent to space returned to Earth with two heads.
The two-headed flatworm was one of 15 launched into space on Jan. 10, 2015 aboard the SpaceX-5 Commercial Resupply Mission. The flatworms were severed at the head and tail, housed in a tube filled half with air and half water, and then spent five weeks on the International Space Station (ISS) U.S. National Laboratory. The experiment helped scientists understand how the microgravity, micro-geomagnetic environment would affect these flatworms. In the meantime, a control group of flatworms remained on Earth.
“During regeneration, development, and cancer suppression, body patterning mechanisms are subject to the influence of physical forces, such as electrical fields, magnetic fields, electromagnetic fields, and other biophysical forces including gravity. We want to learn about how these forces affect anatomy, behavior, and microbiology, as part of harnessing biophysics to control patterning for regenerative applications both on Earth and in space,” said Dr. Michael Levin, director at the Tufts University’s Allen Discovery Center and the corresponding author of the recent journal publication detailing this experiment, published in the April 2017 issue of Regeneration.
Planarian flatworms are known to regenerate all parts of their bodies after injury, but growing a new head is extremely rare under normal conditions. In fact, the researchers said they have never seen it happen spontaneously in the 18 years they have worked with this species. Surprisingly, when the two-headed flatworm was cut into thirds again back on Earth, the middle fragment once again grew back two heads, suggesting a long-term change to the animal’s anatomical blueprint.
But, the two-headed flatworm was not the only change that happened in space:
- Flatworms that traveled to space displayed changes in their behavior even 20 months after their return to Earth. Researchers also observed notable changes in the space flatworms’ microbiota and the chemicals they secrete. A total of 11 proteins were secreted in the space flatworms that were not secreted by their terrestrial counterparts.
- In addition to the severed flatworms sent to space, whole flatworms were sent as well (with a similar control group on Earth). Upon return to Earth, the flatworms’ movement decreased to the point where they were practically immobile and took two hours to display normal movement after being placed in a petri dish with water.
- Space also seemed to alter this creature’s preference for darkness. After returning to Earth, an experiment showed that the space flatworms spent 70.5 percent of their time in the dark, compared to 95.5 percent in flatworms on Earth.
Like slaying the mythical hydra, scientific discovery often leads to more research questions—when one question is answered, more grow from there. This work can help bring scientists closer to transformative advances in regenerative medicine, with applications here on Earth. Scientists hope the flatworm can serve as a model for humans and other space-faring animals, since they are more closely related to mammals than other model organisms, such as Drosophila melanogaster (a fly species) or Caenorhabditis elegans (a roundworm). Additional studies will also help inform future protocols for planarian flatworm studies in space.
View the paper: Regeneration April 2017