According to a recent study , healthy "space mice" were born from freeze-dried mouse sperm that had orbited planet Earth for nearly six years aboard the International Space Station (ISS).
This is good news because DNA-damaging radiation on the ISS is more than 100 times stronger than on Earth.
Future space generations
It is very relevant to examine the effects of space radiation not only on living organisms, but also on future generations if we are to explore space. Space radiation can cause cell DNA damage and effects on the inheritance of mutations in offspring after deep space exploration .
Freeze-dried sperm could potentially play a role in repopulating space colonies.
Most of the studies conducted on the effects of space radiation have not been conducted in space, but under conditions that mimic space. But in the new study, Japanese researchers discovered a novel method of studying radiation in mammalian sperm : they freeze-dried mouse sperm , a technique that allowed sperm to stay at room temperature for more than a year.
That allowed the team to launch the sperm into the ISS without the need for a freezer. Dehydration of the sperm also kept delivery costs low by using "light and small" ampoules to store the sperm.
The sperm were released to the ISS in August 2013 and, once they arrived, the astronauts stored them in a -95 ° C freezer. Some of the samples returned after nine months, others after two years and nine months, and the last of the samples returned after five years and 10 months; the longest biological samples have been preserved in the ISS.
After nine months, the researchers found slightly more damage to sperm DNA and male gamete nuclei than in healthy controls, but fertilization and birth rates were similar.
They found that sperm absorbed about 0.61 millisievert (mSv) / day. By comparison, NASA’s limit for astronauts exposed to radiation in low Earth orbit is about 50 mSv / year, or 0.14 mSv / day.
The researchers found that long-term storage aboard the ISS did not significantly damage the DNA in the sperm . After rehydrating the sperm, they injected it into female mice and found that the mice gave birth to eight healthy pups. Those pups showed no differences in gene expression compared to controls: eight pups were born from sperm cells conserved in the same way on Earth .
The lyophilized sperm showed a "strong tolerance" to space radiation. The authors hypothesize that this could be due to the lack of water molecules within frozen cells; Radiation is believed to induce DNA damage through free radicals, produced when energetic particles interact with water molecules within cells, the researchers wrote.