Nuclear fusion reactions in the sun are the source of heat and light that we receive on Earth. These reactions release an enormous amount of cosmic rays – including X-rays and gamma rays – and charged particles that can be harmful to all living organisms.
Life on Earth is protected thanks to a magnetic field that forces charged particles to bounce from pole to pole and an atmosphere that filters out harmful radiation.
During space travel, however, it is a different situation. To find out what happens inside a cell as they travel through space, scientists send baker’s yeast to the moon as part of NASA’s Artemis 1 mission.
Cosmic rays can damage cell DNA, significantly increasing the human risk for neurodegenerative disorders and deadly diseases, such as cancer. Because the International Space Station (ISS) is in one of Earth’s two Van Allen radiation belts — which provides a safe zone — astronauts aren’t exposed too much. However, astronauts on the ISS experience microgravity, which is another stress that can drastically alter cell physiology.
As NASA plans to send astronauts to the moon, and later to Mars, these environmental stresses become more challenging.
The most common strategy for protecting astronauts from the negative effects of cosmic rays is to physically shield them using state-of-the-art materials.
Lessons from hibernation
Several studies show that hibernators are more resistant to high doses of radiation, and some scientists have proposed the use of “synthetic or induced torpor” during space missions to protect astronauts.
Another way to protect life from cosmic rays is to study extremophiles — organisms that can remarkably tolerate environmental stress. Tardigrades, for example, are micro-animals that have shown astonishing resistance to a number of stresses, including harmful radiation. This unusual firmness stems from a class of proteins known as “tardigrade-specific proteins.”
Under the supervision of molecular biologist Corey Nislow, I use baker’s yeast, Saccharomyces cerevisiae, to study cosmic DNA damage stress. We are participating in NASA’s Artemis 1 mission, where our collection of yeast cells will travel to the moon and back in the Orion spacecraft for 42 days.
This collection contains approximately 6,000 barcoded yeast strains, with one gene deleted in each strain. When exposed to the space environment, those strains would be left behind if the deletion of a specific gene affects cell growth and replication.
My primary project in the Nislow lab is genetically engineering yeast cells to make them express tardigrade-specific proteins. We can then study how those proteins might alter the physiology of cells and their resistance to environmental stress — and especially radiation — in the hopes that such information would come in handy when scientists try to manipulate mammals with these proteins.
When the mission is complete and we have received our samples back, the barcodes can be used to count the numbers of each strain to identify genes and gene pathways essential for surviving damage caused by cosmic rays.
A model organism
Yeast has long served as a “model organism” in DNA damage studies, meaning there is solid background knowledge about the mechanisms in yeast that respond to DNA damaging agents. Most yeast genes that play a role in the response to DNA damage have been well studied.
Despite the differences in genetic complexity between yeast and humans, the function of most of the genes involved in DNA replication and DNA damage response has remained so conserved between the two that we can obtain much information about the DNA damage response of human cells by to study yeast.
Moreover, the simplicity of yeast cells compared to human cells (yeast has 6,000 genes while we have more than 20,000 genes) allows us to draw more solid conclusions.
And in yeast studies, it’s possible to automate the entire process of feeding the cells and stopping their growth in a shoebox-sized electronic device, while culturing mammalian cells requires more space in the spacecraft and much more complex machinery.
Such studies are essential to understand how astronauts’ bodies can cope with prolonged space missions and to develop effective countermeasures. Once we identify the genes that play a key role in cosmic radiation and microgravity survival, we can look for drugs or treatments that can help increase the durability of cells to withstand such stresses.
We could then test them in other models (such as mice) before actually applying them to astronauts. This knowledge may also be useful for growing plants outside of the soil.
By Hamid Kian Gaikani, University of British Columbia