Environmental factors, such as ultraviolet light, can cause DNA damage in organisms. In humans and animals, this DNA damage may cause cancer. Fortunately, cells themselves have several different strategies to repair damaged DNA.
The human beings living on the earth are protected by the atmosphere, thus isolated from most harmful radiation from space. However, the astronauts may be exposed to stronger radiation and therefore face a stronger risk of DNA damage. Now, both the United States and China have announced plans for landing on Mars, so when they are in the microgravity environment of space, what strategies will their bodies choose to repair the DNA damage? Limited to the previous technical barriers, this issue has not been studied.
On June 30, 2021, a paper was published in PLOS One titled A CRISPR-based assay for the study of eukaryotic DNA repair onboard the International Space Station. This research is the first CRISPR gene editing experiment completed in space, laying a foundation for studying DNA damage repair in microgravity environment of the outer space, and is of great significance for human exploration of the vast space, future interstellar travel, and even interstellar migration.
In the International Space Station, limited by various conditions such as experimental equipment, it is difficult to directly observe how cells repair more complex or extensive damage. Therefore, the research team thought of CRISPR, the gene editing technology, using CRISPR to cause precise damage to the DNA of cells, and then astronauts can observe how these DNA damages are repaired on the cells. Astronauts conducted experiments on yeast cells on the International Space Station, cultivating yeast to repair the DNA, extracting the genome, and performing nanopore sequencing on the genome, all of which are carried out in the space-flight environment of the International Space Station.
The research team used auxotrophic yeast, which lacks the URA3 gene necessary for uracil biosynthesis, so it cannot survive and reproduce in normal media. Then, NASA astronauts conducted transformation experiments on these yeasts, introducing URA3 genes, Cas9 genes, and sgRNAs targeting ADE2 genes, as well as repair templates for ADE2 genes. Normally, the colonies formed by yeast on the culture medium are white, but when the ADE gene is mutated, the colonies turn red.
After plasmid transformation, these auxotrophic yeasts can survive and multiply in the medium and form colonies due to the introduction of the URA3 gene. Moreover, red yeast colonies have been observed in the medium, which means that the ADE2 gene editing is successful.
In addition, nanopore sequencing was used to further infer the cell repair mechanism adopted by these yeasts. The sequencing results showed that all the red colonies that were successfully gene-edited had the same gene sequence as the repair template sequence, which indicated that they were all repaired by homologous recombination. This laid the foundation for quantifying DNA repair pathways in the future.
This research has successfully proved the feasibility of this new method, marks the first time that CRISPR/Cas9 has been successfully carried out in space. The research team expressed the hope that this technology can help conduct extensive research on DNA repair in space, and will continue to improve new methods in order to better simulate the complex DNA damage caused by ionizing radiation.
In general, this research not only successfully carried out new technologies such as CRISPR genome editing, miniPCR, and nanopore sequencing in space, but also integrated these new technologies to study microgravity’s effect to DNA repair and other basic cellular processes. This is of great significance for mankind to explore more about human and space.
