Reproduction may be possible in space, Japanese researchers have said, after freeze-dried sperm stored on the International Space Station for nine months produced healthy offspring.
The scientists said their findings could have significant ramifications for human settlements in space, which they consider "likely."
The average daily radiation dose on the ISS is about 100 times stronger than that on Earth, posing a threat of serious reproductive problems for any space-dwelling organism.
But mouse sperm stored on the ISS for 288 days from August 2013 to May 2014, then returned to Earth, fertilized in vitro and transferred into female mice, produced healthy offspring.
Professor Teruhiko Wakayama, of the advanced biotechnology center of the University of Yamanashi in Kofu, told the Guardian that the finding could prove significant if humans started living in space permanently.
"Not necessarily for healthy people -- however, on the ground, many couples require assisted reproductive technology to make babies, and it would continue in the future, including in space.
"Our study suggests that sperm preservation in space is possible for at least nine months."
The space-preserved samples showed evidence of slightly increased DNA damage compared with control samples preserved on Earth, but this was found to be largely repaired in embryos following fertilization.
The birth rate and sex ratio of pups derived from the sperm stored in space was comparable to those of pups derived from the control samples. Subsequent whole genome analysis revealed only minor differences, and the pups developed into adults with normal fertility.
"Although those sperm had a little bit of damage by space radiation, the following offspring were all normal," Wakayama said.
The study was published in the proceedings of the US National Academy of Sciences on Monday.
Wakayama and his fellow researchers predicted that people would live in space for several years or even over many generations, with assisted reproductive technology used to maintain the genetic diversity of humans and animals.
The effects of space radiation and microgravity on mammalian reproduction were largely unknown, but the study of reproduction in space was "a very important subject for our future," Wakayama wrote.
Studies of the effects of microgravity on early development in sea urchins, fish, amphibians and birds had concluded that it did not prevent animal reproduction, but mammals had proved more difficult to keep and test in space.
Humans living for several generations in space habitats, or traveling to Mars, would be exposed to much higher cosmic radiation, which could put them at high risk of cancer.
"The purpose of our project is to know whether mammalian reproduction is possible in space or not," said Wakayama. "Unfortunately, to bring live mice and take care [of them] in space is too difficult. Therefore, we decided on a very simple experiment, which we could perform even with the current technology."
Given the challenging and largely uncharted conditions, researchers were cheered by the findings. How long the sperm could be preserved without damage remained to be seen, Wakayama said, though he was confident that sperm-drying methods would improve.
"Our results demonstrate that generating human or domestic animal offspring from space-preserved spermatozoa is a possibility, which should be useful when the 'space age' arrives."
The next step in the project, already funded by an international grant, would be to send mouse embryos to ISS and culture them under microgravity, he said.
Wakayama has had several high-profile successes in cloning mice, the main area of his research. In 2008, he cloned healthy mice from dead ones that had been frozen for several years, raising the possibility of "resurrecting" extinct animals from their frozen carcasses.
In April last year, he was one of a team of researchers to successfully clone mice from cells found in urine.
"We are now trying to make clone from mouse feces, but so far no success,” he told the Guardian. “I hope you could understand my poor English. English is much harder than to make clone."
© 2017 Guardian Web under contract with NewsEdge/Acquire Media. All rights reserved.