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Why Scientists Sent Mouse Sperm to the International Space Station

Back on Earth, a pile of new pups proves that mouse DNA can survive space

Space mice snuggle with their Earth-bound mother. (Teruhiko Wakayama/PNAS)
smithsonian.com

The idea of traveling to far-flung worlds is tantalizing. But the survival of the human race on these planets is far from guaranteed. Concerns about food and water aside, the species can’t survive if space radiation destroys the DNA in sperm, preventing humans from procreating. Now, that squirmy question is closer to having an answer, reports Katherine Kornei for Science. In their latest test, researchers sent mouse sperm to space. It was successful. Their proof: over 70 newborn mouse pups.

In August 2013, a team of Japanese researchers freeze-dried samples of mouse sperm, then blasted them into space, where they spent over nine months in storage aboard the International Space Station. But for researchers, it was more of a question of damage than storage. Space has no atmosphere to protect DNA from the Sun’s pummeling, destructive radiation; cosmic rays shoot out of deep space with no regard for the building blocks of life. 

Scientists already know that humans are adversely affected by radiation in space, and have spent years devising new ideas for shielding people on eventual long-term missions to Mars and elsewhere. Perhaps the most famous experiment with DNA in space took place when NASA sent astronaut Scott Kelly to the ISS for a year and left his identical twin brother at home on Earth. When Kelly returned, his DNA showed changes. As Smithsonian.com reported earlier this year, his DNA methylation—the way in which DNA controls the expression of genes within cells—decreased, suggesting that space radiation made a difference. A trip to Mars could take as long as eight months, and once on the planet humans would have to contend with a thin atmosphere that could expose their DNA to further damage.

Each sperm cell in a mouse or human contains DNA that hooks up with the DNA in an egg to help build life. But when that DNA is damaged, it can cause birth defects, diseases, and even prevent an animal’s offspring from coming to term.

But in the case of the mice, that didn’t happen. The freeze-dried sperm made its way back to Earth in May 2014. When rehydrated and studied, the DNA did show some damage, including fragmented tails and some breakage. But when female mice were artificially inseminated using the sperm, the fertilized eggs turned into healthy mice pups.

These space pups, as researchers called them, even went on to reproduce and themselves and had healthy mice babies. Seventy-three pups were conceived from the space sperm—equivalent to what you’d expect from Earth sperm. The research team also analyzed their DNA and found that the mice didn’t have any obvious differences. The researchers published their results in the journal PNAS.

The study’s important for a few different reasons. First, it seems that mouse DNA did sustain damage in space—but by the time the space pups were born, they were fine. That suggests that the damage was reparable. Second, it suggests that freeze-dried sperm can survive in space for at least nine months.

So what’s the next step? More research. Scientists need to figure out if deep space—which has even more radiation than near Earth—produces the same changes in mouse DNA. And there’s no guarantee that human sperm will act the exact same way that mouse sperm did, even though mice and humans share an extremely similar genome. You’re likely to see more freeze-dried Thanksgiving entrees in space long before frozen human sperm becomes the norm.  

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