Mouse sperm survives space trip

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Mouse pups derived from space-preserved spermatozoa.
Credit: Teruhiko Wakayama

If the survival of the human race ever comes down to colonising a distant habitable planet, the success of Japanese scientists experimenting with sperm in space may be of monumental significance.

The research team, led by Sayaka Wakayama of the University of Yamanashi, have in one sense gone one step better than the “Plan B” scenario in Christopher Nolan’s 2014 sci-fi epic Interstellar – in which humanity’s survival depends on the transport of thousands of frozen human embryos. Except, of course, their successful breeding program has not involved humans but mice.

The team reports that mouse sperm freeze-dried and carried on board the International Space Station (ISS) for 288 days has been found to be viable on its return to Earth.

The sperm was then successfully used to create fertilised embryos in vitro, which were transplanted to live female mice, the researchers report in the US journal Proceedings of the National Academy of Science (PNAS). The embryos developed into full-term pups and were born healthy.

While on board the ISS, the frozen mouse sperm was exposed to radiation levels about 100 times higher than those experienced by Earth-bound control sperm.

Wakayama and colleagues did discover a small amount of DNA damage when they examined the defrosted ISS sperm prior to fertilisation. This did not, however, translate into abnormalities in the pups, which were born with a gender ratio within the normal range – and grew into robustly fertile adults.

DNA analysis suggests the damage noted before fertilisation was largely repaired during the embryonic stage.

Wakayama and his team conclude the evidence supports the contention that healthy mammalian reproduction is not hindered by using sperm that has endured long periods of being frozen in space.

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