Turns out the comic books were wrong. Japanese researchers found out that mouse sperm exposed to high levels of cosmic radiation for nearly six years produced a large brood of healthy, unremarkable “space pups.”
Their study was published on Friday in Science Advances — which noted no signs so far of “Mousezillas” or “rodent Hulks.” The sperm was stored in the International Space Station (ISS) in freeze-dried form. Once brought back to Earth and rehydrated, it resulted in the birth of 168 mice, free of genetic defects.
Teruhiko Wakayama, a developmental biologist at the University of Yamanashi and lead author of the study, on Thursday said that there was little difference between mice fertilized by space sperm and sperm that had remained confined to Earth.
Photo: AFP / Teruhiko Wakayama, University of Yamanashi
“All pups had normal appearance,” he said, adding that when researchers examined their genes, “no abnormalities were found.”
In 2013, Wakayama and colleagues at the university launched three boxes, each containing 48 ampoules of freeze-dried sperm, to the ISS for the long-term study. They wanted to determine whether long-term exposure to radiation in space would damage DNA in reproductive cells or pass mutations along to offspring.
That could be a problem for our own species in future space exploration and colonization missions.
Batches were returned to Earth for fertilization after the first nine months of the study, as well as after two years and finally after six years, leading to hundreds of births.
Freeze-dried sperm was selected for the experiment because it can be preserved at room temperature, rather than needing a freezer.
The ampoules were also small and very light, about the size of a small pencil, further cutting launch costs.
When the space mice reached adulthood, they were randomly mated and the next generation appeared normal as well.
Wakayama said that he had been inspired by science fiction and once wanted to be an astronaut.
Although he settled on becoming a scientist, the sense of wonder and whimsy about space exploration never left him.
“In the future, when the time comes to migrate to other planets, we will need to maintain the diversity of genetic resources, not only for humans, but also for pets and domestic animals,” Wakayama and colleagues wrote in their paper. “For cost and safety reasons, it is likely that stored germ cells will be transported by spaceships rather than by living animals.”
Getting to other planets means leaving the safety of Earth’s protective atmosphere and magnetic field — which also extends to the ISS, 400km above the surface.
Deep space is filled with strong radiation from solar particles and galactic cosmic rays from outside the solar system.
Solar flares from the surface of the sun generate particles that can have particularly devastating effects on human health and penetrate current spaceships.
The process of freeze-drying sperm increases its tolerance compared with fresh sperm, since the former does not contain water inside its cell nuclei and cytoplasms, Wakayama said.
According to the team’s calculations, freeze-dried sperm could be stored for up to 200 years on board the orbital outpost.
Humanity might also want to spread its genetic resources off-planet in case of a disaster on Earth, the paper added.
The study said that it is still necessary to investigate the effects of space radiation on frozen female eggs and fertilized embryos before humans take this next step into the space age.
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