40 DISCOVERMAGAZINE.COMchair for research at Northwestern University’s Department of
Obstetrics and Gynecology, says mice are so similar that any
problems we’d see in their early pregnancies are likely the same
we’d see in our own. Other researchers agree.
Only mammals have a placenta. So to know the effects of
placenta development in space, we have to use mammals, says
Teruhiko Wakayama, director of the University of Yamanashi’s
Advanced Biotechnology Center in Japan. He’s spent the past
decade studying how mammals — mostly mice — could repro-
duce in space. Without Earth’s gravity pushing everything
down, the need to walk, run and lug around heavy things
goes away in orbit. Consequently, so do our strong bones and
muscles. Since this strength is important for pregnancy, and
essential for a growing fetus, Wakayama wanted to see if mice
could even become pregnant under these conditions.
In 2009, Wakayama extracted eggs and sperm from mice,
then set them loose in a device that simulates microgravity
(the technical term for orbiting astronauts’ weightlessness). He
watched the sperm swim into the eggs, and after a few days of
microgravity, he and his colleagues implanted the embryos into
female mice in standard gravity. The results were mixed: While
many normal, healthy pups were born, a lot of the embryos
didn’t develop properly after implantation. As a result, the mice
had fewer offspring than mice in regular gravity.
To see if these results hold up in space, where high radiation
levels accompany microgravity, Wakayama reached out to
the Japan Aerospace Exploration Agency about replicating
his study on the International Space Station (ISS). But this
time, astronauts would extract the sperm and eggs from living
mice, then transfer the fertile embryos back into mice, all in
microgravity. That plan proved too difficult, so the mice never
made it to space. Their sperm, on the other hand, did.
Wakayama, who’s now the principal investigator of NASA’s
Space Pup mission, freeze-dried mouse sperm and preserved it
at room temperature. Three sets of these freeze-dried samples
went to the ISS in 2013, and he’ll study their viability after
different lengths of time on the space station. It’s not the same
as studying fertilization and pregnancy under microgravity,
but this work allows astronauts to analyze the effects of space
radiation on male reproductive cells.
The ISS is exposed to strong space radiation that may break
sperm DNA, and the resulting offspring may be changed,
Wakayama says. Not much research has looked at the health
of mice made with damaged DNA, but Wakayama is slowly
answering those questions.
After staying on the ISS for nine months, some of that spermshowed signs of slight DNA damage, yet went on to produce
normal, healthy pups. Wakayama’s team is just now analyzing
samples that flew on the ISS for three years; the final batch, in
space for six years, is set to return to Earth this spring.
If his freezing technique works, Wakayama plans to haul
frozen mouse embryos to the ISS to investigate the next part
of the problem: finding out why they’re not fully developing
in space.FROM MICE TO MARTIANS
Mice may be one of the best models of human reproduction in
space, but despite the similarities, they’re still a far cry from an
actual human.
Joseph Tash, a reproductive biologist at the University of Kansas
Medical Center, points out that without functional human sperm
and eggs, our settlements won’t last long in space. He’s been work-
ing with NASA since 1996, and until a few years ago, his research
mainly focused on the effects of spaceflight on mice and other ani-
mals. But in April 2018, he used a method similar to Wakayama’s
and launched frozen sperm into space — this time, it was human.
The experiment, dubbed Micro-11, collected top-notch
sperm from 12 healthy, fertile men. In a lab aboard the ISS,
astronauts thawed the frozen samples and mixed them with a
chemical cocktail that spurred the sperm to start swimming.
Essentially, the mixture’s chemical signals tricked the sperm
into thinking they were heading toward an egg. Then astro-
nauts filmed the movements using a high-powered microscope,
trying to capture whether the sperm were physically capable
of fertilizing eggs in space.
“There are various changes in the appearance of the sperm
when you look under a microscope,” Tash says. “You can see very
specific changes to the head of the sperm that are required for the
sperm to fertilize an egg.” The swimmers need to gain speed as
they get closer to their target, and the cells in their heads need to
merge together so they’re strong enough to break through the egg.
If they don’t, pregnancy is a no-go.
The samples are now back on Earth, but Tash says it will take
another year to comb through observations of their tiny reproduc-
tive motions and determine if the space sperm would make the
cut. Once Micro-11 is complete, though, he’s jumping right into
the next cosmic conundrum: female fertility in space.
He’s already found some reasons to worry. Tash studied female
mice that went on NASA space shuttle trips back in 2010 and 2011.
He discovered that their corpora lutea — short-lived glands in the
ovaries responsible for producing sex hormones and nurturing
nascent embryos — changed for the worse.Space Radiation 101
Beyond the protection of Earth’s
atmosphere, Martian residents will be
pelted with dangerous, high-energy
radiation. It blazes from our sun during
fiery solar flares, and is also thought
to blast from distant supernova
explosions. These cosmic rays are
made up of atomic nuclei (protons
and neutrons) and electrons, which
get knocked out of the atoms as they
fly through space at nearly the speed
of light.
After the electrons are gone, the
remaining particles become ionized,
ready to transfer energy to nearby
objects. This powerful radiation canpenetrate a spacecraft or an astronaut’s
body without pause. When it comes
in contact with humans, the rays can
wipe out the electrons in their cells.
This bombardment is known to damage
the structure of DNA and cause cells to
mutate or die off altogether, increasing
astronauts’ risk of disease. — A.J.