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Mouse pups born from sperm stored on the International Space Station for 9 months. 

S. Wakayama et al., Proceedings of the National Academy of Sciences 114, 21 (23 May 2017) © 2017 National Academy of Sciences

Sperm frozen in space produce healthy mouse pups

If NASA wants to send humans to Mars, it will probably also send along an unusual provision for the interplanetary journey: sperm. A diverse supply of human sperm could ensure the genetic diversity of a new colony, which is critical to a healthy population. But no one knows whether the reproductive cells could withstand the ravages of DNA-damaging radiation in space. Now, a new study shows that mouse sperm stored for more than 9 months on the International Space Station (ISS)—where radiation levels are roughly 100 times higher than on Earth—can produce healthy, fertile mouse pups.

“This work is enormously important,” says Steven Peck, a biologist and bioethicist at Brigham Young University in Provo, Utah, who was not involved in the research.

Researchers led by Teruhiko Wakayama, a biologist at the University of Yamanashi in Kofu, Japan, sent freeze-dried sperm from 12 mice to the ISS in 2013. Astronauts placed the samples in a freezer at –95°C, where they remained for 288 days. On Earth, the team stored sperm from the same mice at the same temperature for the same amount of time.

When the space-faring samples were returned to Earth, Wakayama and his colleagues looked for signs of DNA damage caused by radiation. As expected, the ISS sperm exposed to the higher levels of space radiation near the station exhibited more fragmented DNA than the Earth-bound sperm. This DNA damage, which would have been impossible for the frozen cells to repair, has been associated with lower levels of fertility. But when the scientists injected the space sperm into fresh mouse eggs that they transferred into surrogate mothers, they were in for a surprise. Roughly 3 weeks later, the females gave birth to 73 “space pups,” about as many as they would have expected from normal sperm, the team reported today in the Proceedings of the National Academy of Sciences. That’s the first time such an experiment has been done for any mammalian species, Wakayama says.

The mice sired from the experimental sperm were fertile and healthy, and there were no obvious genetic differences between the space pups and their control brethren, Wakayama and his colleagues showed. The study suggests that the DNA damage was repaired after fertilization, and that it has “no ultimate effect” on the offspring, the team writes.

That’s good news for the space pups, but also for the many human astronauts who have gone on to become parents after spending time in space. But there’s still a lot to do before astronauts start packing for Mars, the team notes. Scientists need to study sperm from other mammalian species held in space for longer periods of time. They also need to conduct studies in more realistic deep-space conditions, says biophysicist Francis Cucinotta of the University of Nevada in Las Vegas, who was not involved in the research. “The most damaging radiation is found outside the Earth’s geomagnetic shielding,” far beyond the orbit of the ISS, he says. “There are much higher risks in deep space.”