Astronaut Loral O'Hara works inside the Microgravity Science Glovebox. Credit: NASA
In a first, Japanese scientists and astronauts have successfully grown mouse embryos on the International Space Station in microgravity. The successful results may have big implications for future human reproduction in space.
Previously, the impact of microgravity on embryo development had only been reported in sea urchins, fish and amphibians. And while the more data the better, mammalian reproduction is complicated, highly specialized and unlike that of other taxa.
Additionally, the same group of researchers behind this new study previously conducted an experiment on mammalian embryonic development in vitro under simulated microgravity conditions. However, the results exhibited significant anomalies and were inconsistent. Thus, the University of Yamanashi researchers knew they needed to assess the impact of actual space—though that was easier said than done since frozen embryos can only be thawed and cultured by trained laboratory professionals, not ISS astronauts.
To address this limitation, the researchers developed a new embryo thawing and culture unit (ECT) to allow the thaw and culture of frozen mouse 2-cell embryos on the ISS without necessitating astronauts directly come into contact with the embryos.
For the project, named “Space Embryo,” the University of Yamanashi team prepared eight ETCs with 90 embryos each for transport to the ISS. The embryos were launched to the ISS on Aug. 28, 2021 by Space X 23, and transported to the station the next day.
On September 4, the culture medium was placed in a carbon dioxide incubator for gas equilibration. Then, two days later, the experiments officially began. Eight ETCs were thawed by an astronaut—four were cultured in microgravity, while the other four were cultured in artificial-1 g. Four days later, PFA was injected into the ETCs to fix the embryos, and PFA was replaced with PBS. The ETCs were then refrigerated until their return to Earth. All ETCs were recovered safely from the return vessel that splashed downed on Earth on September 30, a little over a month before the embryos started their journey to space.
According to the study’s findings, published in iScience, 72 (20%) of the embryos were recovered from the microgravity conditions. Of those 17 formed blastocysts, the cells that develop into the fetus and placenta. Thirty-two stopped development at the 2-cell stage, 10 at the 3/4-cell stage and 5 at the 8-cell stage.
Although the rate of formation of blastocysts was low, the authors did conclude that two-cell mouse embryos could develop blastocysts in microgravity on the ISS. Additionally, there were no significant changes in the condition of the DNA and genes. In fact, while the team did find 13 genes that were differently expressed in the ISS group compared with ground controls, none of the genes showed significant different and no common negative trend was found. The researchers also concluded that space radiation did not negatively affect the blastocysts.
However, all blastocysts did show evidence of bacterial contamination
“This must have been a significant factor in the decreased rate of development of the blastocysts,” said the researchers.
In future research, the scientists say they would like to transplant the blastocysts cultured in ISS's microgravity into mice to confirm that the blastocysts can grow into fully developed children.