On May 22, 2019, then-Queen’s University researcher Aaron Rosenstein boarded a modified Falcon 20 aircraft at the Ottawa airport for an up-and-down parabolic flight, during which he and fellow researchers experienced up to 20 seconds of microgravity conditions at a time.
Rosenstein’s goal was to build on decades of studies into DNA. The result?
The student observed that changes in DNA replication had occurred during the brief microgravity mission, and the work that came out of this flight garnered him lead author status of a peer-reviewed study, published in the journal Frontiers in Cell and Developmental Biology this past November.
What exactly is DNA and what does it do?
Rosenstein — who earned his master of science at Queen’s in 2020 and is now a bioengineering doctoral student at the University of Toronto — said DNA is the blueprint of life and a sort of instruction manual that tells cells what to do, when to do it and how to do it. As cells divide, they copy DNA and continue that process throughout a person’s lifetime.
“That process of copying DNA is really important,” Rosenstein told SkyNews, as it ensures basic cell functions to replace older, dead or damaged cells — even for processes as simple as healing a skinned knee.
Rosenstein’s role on the flight was to not only battle the inevitable nausea from going up and down so often, but also to look at enzymes, or “molecular machines,” as he calls them.
“It’s kind of like a really small robot that our cells generate, and there’s tons of different designs out there,” he explained of enzymes. “One class of enzymes are called DNA polymerases. So DNA is a polymer, and polymer is kind of like a scientific name for beads on a string – meaning that it’s kind of like a big molecule that’s made up of small building blocks.”
DNA polymerase, he explained, is an enzyme that copies DNA. The “double helix” molecular structure of DNA constrains two long strands. Polymerase uses half of the helix — one strand — to copy to the other.
“Generally our DNA polymerases are very accurate, because the cell wants to maintain the DNA sequence that it has right now,” Rosenstein said. “The sequence we have lets us function and prevents us from acquiring diseases. A lot of disorders and a lot of diseases are caused by having mutations.”
The major danger to DNA in space is radiation, which increases the risk of lifetime cancer. That said, NASA and other spaceflight agencies have numerous measures in place to protect astronauts. This includes monitoring radiation conditions on the space station, having protocols in place to take shelter during major radiation events such as solar storms, and imposing lifetime radiation limits on astronauts.
What microgravity does to DNA
Rosenstein’s research on polymerase suggests a far more subtle change to DNA than radiation.
Even in Earth conditions, DNA polymerase does not copy perfectly. Sometimes, in one of a few million cases, it will make an error in the copying. It’s a well-known phenomenon that has been studied on our planet for decades, but Rosenstein noticed that little research was known about this copying process in microgravity.
Hence his plane ride.
Sitting (or as the case may be, floating) on a big box beside him was a self-contained environment where Rosenstein would start and stop reactions to copy DNA. He was careful to do this process only during microgravity phases of the flight, because otherwise any errors induced may be due to other factors.
“We had our single-stranded piece of DNA in one tube, and our enzymes in the other tube,” Rosenstein said of the experiment. “Then when we got into microgravity, we mixed them all together. DNA polymerase is really fast. So in the span of 20 seconds, you can copy about 200 to 300 base pairs of DNA … and there’s not just one molecule in each tube. There’s trillions of molecules, so you’re copying a lot of DNA all at once.”
By the time he got off the plane, Rosenstein had a large set of double-stranded DNA, all replicated in microgravity.
After months of analysis, he noticed that the DNA polymerase active in microgravity appears to introduce more errors into the strand than in Earth conditions, but there are several cautions associated with the finding.
First, radiation remains a far more pressing danger to astronauts. Second, Rosenstein was only looking at a specific conversion mutation between a certain base and another base; only one kind of enzyme was studied, and thus this only describes perhaps a specific type of mutation. He also noticed the kinds of microgravity mutations that occur are different than on Earth, but given this is a single study, more work would be needed.
“To say that this is some sort of cause of increased mutation in space, I think would be benign,” Rosenstein said of his findings. In other words, just because polymerases may be less accurate in microgravity is not necessarily a cause of mutations — especially concerning mutations in terms of astronaut health — during spaceflight.
One possible implication from his study is perhaps — still to be confirmed — that human DNA might be less effective at repairing radiation damage in space due to the lower polymerase accuracy Rosenstein found. Again, though, there is no indication of concern at this time.
“The major source of DNA damage and DNA mutations in space is going to be radiation. It’s not going to be DNA polymerases,” he said. “So to take this out of context, and say that polymerases are the cause of mutations in space, is not fair — and it’s not true.”
Cell behaviour in microgravity and radiation exposure’s effect on genes
Another major source of context is understanding that cells in general behave differently in microgravity, although not necessarily in a concerning way. Cells that are mobile, for example, do not adhere to surfaces in the same way. Rosenstein says that this behaviour comes down to enzymes, proteins and other lower-level life processes that cause these observed abnormalities.
“So the fact that we saw altered enzyme function in microgravity is an indication that this may be a fruitful effort [to understand] other enzymes and other processes,” Rosenstein said. He pointed out that the layperson may focus on the copying errors he found, while scientists would likely be more interested in the implications of how basic life functions work in spaceflight.
Rosenstein’s research also focuses on levels of “expression” in genes, or how they are turned on and off. Alterations in gene expression was a finding of the “twins study” that featured NASA astronaut Scott Kelly — in space for almost an entire year in 2015-16 — and his twin brother Mark Kelly, a then-retired NASA astronaut who was tested on the ground during the same time period as Scott’s spaceflight.
A 2019 Science paper noted both Scott and Mark had changes in gene expression during the study period, but not the same changes. “Changes Scott experienced may have been associated with his lengthy stay in space,” NASA said in a press release about the mission findings to that date.
“Most of these changes — about 91.3 per cent — reverted to baseline after he returned to Earth,” the agency continued. “However, a small subset persisted after six months. Some observed DNA damage is believed to be a result of radiation exposure.”
Rosenstein described the gene expression piece of spaceflight as a huge puzzle in which different teams are trying to examine the pieces. “I might see something over here — an effect in microgravity — and somebody else might see another effect over there that is completely seemingly unrelated,” he said.
“There is a really complex network of genes that all function in concert together and that all impact each other,” he continued. “Understanding how those interactions occur and why they occur, and how they impact cellular dysfunction in space is interesting.”
Rosenstein said that more broadly, he is interested in seeing how changes in gene expression impact the cell’s ability to survive microgravity, which down the road may help with “gene therapies” to assist astronauts on long-term space missions. But at the time of the interview, he was focused on finishing his thesis and hoping for a second flight opportunity someday.
“It’s a ton of fun,” he said of the experience, but he joked that a second flight would have been preferable. Rosenstein said it was at least somewhat stressful that his “entire master’s thesis depended on it … working over the course of a few hours.”
This biweekly column by Canadian science and space journalist Elizabeth Howell focuses on a trending news topic in Canadian astronomy and space.