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To ensure the long-term survival of humankind, we might as well shoot for the Moon.
In 2013, Japanese researchers did just that by launching freeze-dried mouse sperm into space. The goal was to see if mammalian swimmers can maintain their spunk amid harsh cosmic radiation—which they’ll undoubtedly have to endure for humans to thrive in the coming space age. The result: after nine months on the International Space Station (ISS), sperm did show signs of DNA damage, but they were still able to produce healthy, fertile offspring.
This is good news, the authors explain in PNAS. “In the future, humans likely will live on large-scale space stations or in other space habitats for several years or even over many generations,” they write. To maintain genetic diversity in small colonies, treat infertility, and breed domestic animals in our future interstellar homes, preserved sperm and eggs may be critical.
But it wasn’t clear before this study that sperm were up for the task. Space radiation can cause DNA damage, which could lead to mutations and tumors. In sperm, that could mean spontaneous abortions or mutated offspring.
To see if that was the case, the researchers blasted some freeze-dried mouse sperm up to the ISS and kept a second batch on Earth. The researchers went with freeze-drying rather than cryopreserving to keep costs low—there was no need to launch a heavy freezer into space. Freeze-drying kills sperm, but its preserved contents can still be used to fertilize an egg.
While on the ISS from August of 2013 to May of 2014, the space sperm were exposed to radiation levels about 100 times higher than those on Earth. This caused noticeable, but relatively minor, DNA damage.
Back on Earth, the researchers rehydrated the sperm and squirted them directly into fresh egg cells. The researchers then transferred the resulting embryos into female mice. From there, embryos fertilized with space sperm had roughly the same birth rate as those fertilized with ground-control sperm, 8 to 17 percent and 7 to 15 percent, respectively. In the end, the researchers had 73 “space pups” that went on to be healthy mice. Tests showed that the mice had normal gene activity and fertility rates.
The researchers speculate that—although the space sperm’s DNA was damaged and would not get repaired because the freeze-dried cells were dead—the damage was likely repaired after fertilization. While this raises prospects for future space-sperm preservation, the authors note that more studies are needed to assess the effects for human sperm, longer space time, and trips deeper into space, where there’s more radiation.
Still, the authors are optimistic that we’ll have things figured out before the space age arrives. In fact, they even have ideas for the first interstellar sperm bank:
Once the reliability and integrity of space-preserved spermatozoa can be demonstrated, underground storage on the Moon, such as in lava tubes, could be among the best places for prolonged or permanent sperm preservation because of their very low temperatures, protection from space radiation by thick bedrock layers, and complete isolation from any disasters on Earth.
PNAS, 2017. DOI: 10.1073/pnas.1701425114 (About DOIs).