20 June 2021
Japanese researchers have successfully produced healthy mice from frozen sperm that was stored on the International Space Station (ISS) for almost six years.
The sperm was freeze-dried and sent to the ISS in 2013. Freeze-drying is a process that removes water from frozen substances in an effort to make them last for a long time.
Once the sperm was brought back to Earth and unfrozen, it resulted in the birth of 168 healthy baby mice. The researchers said there was little difference between the mice produced by space sperm and those made with usual sperm.
Teruhiko Wakayama is a developmental biologist at Japan's University of Yamanashi. He was the lead writer of a study reporting the results in Science Advances.
"All pups had normal appearance," Wakayama told the French news agency AFP about the experiment. When researchers examined genes of the mice "no abnormalities were found," he said.
The team launched three containers, each carrying 48 samples of freeze-dried sperm, to the ISS in 2013. Freeze-drying permits substances to survive at room temperature for up to a year so no freezer was needed on the launch rocket. On board the ISS, the samples were kept inside a freezer at minus 95 degrees Celsius.
Samples were returned to Earth at different times. The first were flown back after nine months and the second after two years. When the last container returned to Earth in June 2019, it had spent 5 years and 10 months in space. The returned samples were injected into egg cells, which were put inside female mice.
The experiment aimed to find out whether taking in radiation for long periods in space would damage DNA in reproductive cells or pass on mutations to babies. This same issue could be a problem for humans in the future if space exploration greatly expands, with large populations possibly living on other planets.
Deep space is filled with high radiation produced by solar particles and cosmic rays from outside our solar system.
The researchers said the sperm cells experienced radiation levels 170 times greater than sperm kept in ground storage for comparative purposes. The researchers reported that the space radiation did not damage the sperm's DNA or reduce its fertilization ability compared to the sperm kept on Earth.
"In the future, when the time comes to migrate to other planets, we will need to maintain the diversity of genetic resources," Wakayama wrote in a paper on the experiment. He added that such diversity -- both in humans and animals – can protect against increases in harmful mutations seen in inbreeding.
Wakayama said carrying freeze-dried reproductive cells from large numbers of individuals would be easier and less costly than transporting people or animals themselves to space. This method could permit space colonies to develop that include animals, he added.
The researchers say their results suggest that freeze-dried sperm could be effectively stored on the ISS for up to 200 years.
I'm Bryan Lynn.
Bryan Lynn wrote this story for VOA Learning English, based on reports from Reuters, Agence France-Press and Science Advances. Caty Weaver was the editor.
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Words in This Story
sperm – n. a small cell produced by a male animal that joins an egg from a female animal to create a baby
pup – n. a young dog or other kind of baby animal
sample – n. a small amount of something that shows what the thing is like
mutate – v. to cause (a gene) to change and create an unusual characteristic in a plant or animal : to cause mutation in (a gene)
cosmic rays – n. high-energy particles that move through space at nearly the speed of light
maintain – v. to make something continue in the same way
diversity – n. a situation in which many different kinds of things or people are included in something
inbreeding – n. a situation in which plants, animals or people are produced by breeding between closely related plants, animals or humans