The longest biological experiment ever on the International Space Station has revealed the surprising durability of freeze-dried mouse sperm when exposed to space radiation.
The year is 2189. With the launch of Generation Starship Tycho a few months later, the pace of preparations had taken on a breakneck pace. Operations Director Prisha Tengku was finalizing the installation of 10 exosomatic uterine chambers when she noticed a strange box tucked away in a corner of the cryogenics lab. Curious about its contents, Tengku examined the box and found 10 glass vials filled with a whitish substance. The labels identified the boxes as containing freeze-dried human semen, which had been prepared in 2038 and kept on board the Lagrange2 III space station since that time.
Tengku was immediately tempted to throw away the 151-year-old samples. There is no way, she thought, that the sperm exposed in space for so long could survive all this radiation. In addition, the lyophilized samples were stored at room temperature, without any special protective envelope. Cleverly, however, she decided to check the literature to see if an expiration date existed for this sort of thing. Nothing in recent scientific literature appeared, so she expanded her research, culminating in the discovery of an obscure 2021 article that appeared in Science Advances.
the paper, co-authored by Teruhiko Wakayama of the Center for Advanced Biotechnology at Yamanashi University in Japan, describes an experiment in which freeze-dried mouse sperm remained viable after spending nearly six years aboard the International Space Station. Space ionizing radiation is known to damage cellular DNA, triggering potentially deleterious hereditary mutations. The researchers set out to determine the long-term effects of space radiation on mammalian sperm stored on the International Space Station and how this exposure might affect normal reproduction.
It was the same orbital station, Tengku recalls, which was wiped out by stray space debris in 2029. She paused, realizing that Wakayama and her colleagues were doing important work, setting the stage for long-range space missions. to the Moon and Mars – and now the impending launch of Generation Starship Tycho towards interstellar space. Digging deeper, Tengku found a June 2021 interview with Wakayama, in which he wrote to Gizmodo science reporter George Dvorsky in an email.
“Hundreds of years from now, when humans live on another planet, we will have to bring domestic animals, such as dogs and cats,” Wakayama wrote. “To maintain these species or strains, we will have to bring a lot of animals to avoid inbreeding, but it will cost too much. However, if you bring freeze-dried sperm – and oocytes if possible – you can maintain these species without the cost of transportation. “
Theoretically, the same strategy could apply to humans, if future space explorers needed a safe, inexpensive, and convenient way to store sperm.
It is not easy to study this stuff, because the ISS lacks freezers, and transporting liquid nitrogen tanks into space is expensive and expensive. Instead, Wakayama and his team came up with the idea of freeze-drying mouse sperm as a surrogate, as these samples can be easily stored at room temperature and would not require constant astronaut attention. The unprotected samples remained on the space station for years, slowly absorbing space radiation.
The freeze-drying process used in the study “is similar to instant coffee or freeze-dried fruit,” Wakayama explained. “You only have to add water”, and it can be used “immediately”. The freeze-drying process kills the sperm, but when it is rehydrated and injected into a mouse egg, the sperm can still fertilize the egg, which then develops normally, he said.
For the experiment, freeze-dried sperm samples from 12 mice were shipped to the ISS in small, lightweight capsules. Identical samples, which served as controls, were stored at the Japanese Space Agency’s Tsukuba Space Center under similar conditions, except for exposure to space.
In 2014, exactly nine months later, some samples were sent back to Earth to see if the experiment was working, which it was. Another batch was sent back to Earth after two years and nine months, and the last batch after five years and 10 months, which occurred in 2019. This is the longest biological experiment ever on the ISS. .
Back on Earth, Wakayama and his colleagues studied sperm, measuring the amount of radiation absorbed by the samples. They performed tests to see if the DNA in the semen nuclei had been damaged, finding that the radiation had minimal effect. The embryos produced by the rehydrated sperm were slightly inferior in quality to those of the controls on Earth, but, surprisingly, they developed into 168 baby mice, all of whom looked normal. Further analysis of baby mice with RNA sequencing tools showed no abnormalities in gene expression. Some of these mice were bred to maturity and were able to produce healthy babies on their own.
The team also performed a ground control experiment, in which freeze-dried sperm were exposed to x-rays. The experiment showed that freeze-dried sperm “has a high tolerance to radiation,” Wakayama said. This result, combined with the findings from the ISS experiment, led the team to conclude that “sperm can be stored for at least 200 years on the ISS,” as he explained.
Once this experiment is complete, Wakayama is already planning to perform similar experiments on the NASA-proposed Gateway Lunar Space Station, which is expected to be orbiting the Moon.
“In space, there are two different environments: one is spatial radiation and the other is weightlessness (…) and we want to know whether mammalian embryos can develop in weightlessness or not”, a he said, adding that the proposal for this experiment approved by NASA and JAXA in 2015. He noted that early-stage frozen mouse embryos are expected to be launched to the ISS in August 2021, which astronauts thaw and grow in zero gravity. Wakayama said he “can’t wait” to see the results of this experiment.
After completing his research on the matter, Tengku again examined his 151-year-old freeze-dried semen samples. As the old Science Advances article suggested, they should still be correct and even last for another 50 years. Decades later, when GS Tycho was still en route to the exoplanet Kepler-452b, Tengku used those samples to produce the crew’s Wallace population, but that’s a different story.
After: First detailed study of mouse behavior in space reveals weird, coordinated zoom.