The longest-running biological experiment ever conducted on the International Space Station has revealed the surprising durability of freeze-dried mouse sperm when exposed to space radiation.
It’s the year 2189. With the release of Generation Starship Tycho just a few months away, the pace of preparations has taken on a frenetic pace. Operations Director Berisha Tingkou was finishing the installation of 10 external uterine chambers when she noticed a strange chest hidden in the corner of Cryogen’s lab. Tengku, curious as to its contents, examined the box and found 10 glass ampoules filled with a white substance. The labels specified that the containers contained freeze-dried human sperm, which was prepared in 2038 and has been kept aboard the third space station Lagrange 2 since that time.
Tengku was immediately tempted to discard the 151-year-old specimens. There is no way, he thinks, that sperm exposed to space for so long could survive all this radiation. Furthermore, the lyophilized samples were stored at room temperature, without a special protective wrap. However, he cleverly decided to review the literature to see if there was an expiration date for this kind of thing. Nothing has appeared in the recent scientific literature, so he expanded his research, leading to the discovery of a mysterious article from 2021 that appeared in Science Advances.
The Article – Commodity, co-authored by Teruhiko Wakayama of the Center for Advanced Biotechnology at Yamanashi University in Japan, describes an experiment in which freeze-dried rat sperm remained viable after spending nearly six years aboard the International Space Station. Ionizing space radiation is known to damage cellular DNA, resulting in genetic mutations that can damage. The researchers aim to determine the long-term effects of space radiation on mammalian sperm stored on the International Space Station and how such exposure might affect normal reproduction.
Tongko eerily recalls that it was the same orbital station that was wiped out by unwanted space wandering in 2029. He pauses and realizes that Wakayama and his colleagues are doing important work, paving the way for long-term space missions to the Moon and Mars. And now the imminent launch of Generation Starship Tycho into interstellar space. Going deeper, Tengku found an interview in June 2021 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 in pets, like cats and dogs,” Wakayama wrote. “To maintain these species or breeds, we would have to bring in a lot of animals to avoid inbreeding, but that would be very expensive. However, if you bring in freeze-dried sperm, and eggs if possible, you can keep these species without the cost of transportation.”
In theory, the same strategy could be applied to humans, should future space explorers need a safe, cheap, and convenient way to store sperm.
It’s not easy to study these kinds of things, the International Space Station has a shortage of freezers, and moving liquid nitrogen tanks into space is expensive and cumbersome. Instead, Wakayama and his team came up with the idea of freezing rat sperm as an alternative, as these samples could easily be stored at room temperature and would not require constant attention from astronauts. Unprotected samples simply stayed on the space station for years, slowly absorbing space radiation.
Wakayama explained that the freeze-drying process used in the study “is similar to instant coffee or freeze-dried fruit.” “Just add water” and it can be used “immediately”. The freeze-drying process kills the sperm, he said, but when it is rehydrated and injected into a mouse egg, the sperm can still fertilize the egg, which then develops normally.
For the experiment, freeze-dried sperm samples from 12 mice were shipped to the International Space Station in small, lightweight capsules. Identical samples, which served as controls, were stored at the Japan Space Agency’s Tsukuba Space Center under similar conditions, except for space exposure.
In 2014, exactly nine months later, some samples were returned to Earth to determine if the experiment had been successful, and it did. Another batch was returned to Earth after two years and nine months, and the final batch after five years and 10 months, which occurred in 2019. It is the longest-running biological experiment ever on the International Space Station.
Back on Earth, Wakayama and his colleagues studied the sperm and measured how much radiation the samples absorbed. They ran tests to see if the DNA in the sperm nuclei had sustained any damage, and found that the radiation had little effect. The embryos produced by the rehydrated sperm were slightly inferior in quality compared to the ground controls, but surprisingly, they grew into 168 young mice, which all appeared normal. Further analysis of young mice using RNA sequencing tools showed no abnormalities in gene expression. Some of these mice were bred to maturity and were able to produce healthy children.
The team also conducted a soil control experiment, in which freeze-dried sperm was exposed to X-rays, and this experiment showed that freeze-dried sperm “has a high radiation tolerance,” Wakayama said. This finding, along with the results of the ISS experiment, led the team to conclude that “sperm can be preserved for at least 200 years on the ISS,” he explained.
With this experiment complete, Wakayama is already looking to conduct similar experiments on NASA’s proposed Gateway Lunar Space Station, which is slated to be placed in lunar orbit.
He said, “In space, there are two different environments: one is space radiation and the other is zero gravity … And we want to know whether or not mammalian embryos can develop under zero gravity.” The experiment was approved by NASA and JAXA in 2015. He noted that frozen early-stage rat embryos will be released to the International Space Station in August 2021, which astronauts will thaw and grow under zero gravity. Wakayama said he “can’t wait” to see the results of this trial.
After completing his research on the topic, Tengku revisited the 151-year-old’s freeze-dried sperm samples. As the old Science Advances article suggested, they should still be fine and even last another 50 years. Decades later, when GS Tycho was still on its way to the exoplanet Kepler-452b, Tengku used these samples to produce the population of Wallace’s crew, but that’s another story.
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