A very long vacation aboard the International Space Station did not result in excessive damage to freeze-dried sperm.
The most well-travelled mouse sperm in history left Earth in 2013 on its return trip to the International Space Station (ISS). After spending nearly six years on the station, the freeze-dried sperm were returned to Earth in 2019 in a SpaceX cargo capsule and used to breed healthy “space pups.”
The study, published Friday in the journal Science Advances, details space sperm experiments, which were conducted by a team of Japanese researchers aimed at understanding the long-term effects of space radiation on mammalian sperm. The freeze-dried sperm were sent to the ISS and spent nearly six years in the orbiting laboratory, traveling around Earth at a distance of about 250 miles.
What did the researchers do? The researchers collected sperm from male rats and placed them in ampules — tiny glass vials — before freeze-drying them to remove all the water. They stored freeze-dried (FD) sperm in freezers on the International Space Station and, in parallel, on Earth. Some sperm were returned after nine months on the ISS to check that everything was working as planned, but two other groups of samples spent days 1010 and 2129 on the station.
Once returned, the sperm were re-sterilized and a type of mouse IVF was performed to impregnate female mice with space sperm and Earth sperm. The females then delivered their litters and the space pups were compared to “ground control” pups.
“The space puppies showed no difference compared to the ground control puppies, and they also had no abnormalities in their next generation,” the team wrote.
The researchers also assessed whether space sperm differed from sperm stored on Earth by examining damage to their DNA and gene expression. Under a microscope, the space sperm looked very similar to Earth spermatozoa and the team also reports that the space sperm exposed to radiation suffered no additional DNA damage. Gene expression profiles were unchanged.
How does it matter? “Space wants to kill you” is a phrase thrown around a lot—and for good reason. Space radiation blasts through almost everything in the universe and, without adequate protection, it can collide with DNA causing breakage and mutation. Researchers don’t see DNA damage in freeze-dried sperm, which is a big win.
Researchers say the freeze-drying process, which removes water from their sperm samples, may have a protective effect against DNA damage because some of this damage results from water within sperm cells.
However, the ISS is much closer to Earth and is shielded from particularly dangerous space radiation by the planet’s magnetic field. Whether deep-space exploration will cause more trouble for freeze-dried sperm is an open question.
In the distant future, perhaps, we could even build a kind of frozen Noah’s Ark in space, in case we experience some terrifying, apocalyptic crash in the biodiversity of the many species stored underground on the Moon. With freeze dried sperm (climate change can wreak that kind of havoc).
What will happen next? NASA and other space agencies around the worldA space station that will orbit the Moon and serve as an outpost for human travel across the Solar System. In their closing remarks, the researchers suggest that freeze-dried sperm experiments may also be conducted at the Gateway to test the effects of space radiation beyond Earth.