Newsweek headlined its article, “Scott Kelly: NASA Study Confirms Astronaut’s DNA Actually Changed in Space.” The article says:
After landing, 93 percent of Scott Kelly’s genes returned to normal, the researchers found. The altered 7 percent, however, could indicate long-term changes in genes connected to the immune system, DNA repair, bone formation networks, oxygen deprivation and elevated carbon dioxide levels.
The Telegraph headline reads, “Nasa astronaut twins Scott and Mark Kelly no longer genetically identical after space trip.” The article states:
But new findings by Nasa have found that life away from planet Earth has exacted a surprising toll. The pair are no longer genetically identical twins.
Please understand that both of these articles are doing what is typical of the modern media when it comes to science. They are taking results that are really, really interesting, and they are hyping the results to the point where they are not telling the truth anymore. NASA did do a wonderful experiment on the genetic effects of being in space a long time, and while the results are quite remarkable, they don’t indicate that space changes a person’s genes. They indicate that space changes the expression of certain genes, and for some, that change is remarkably long-lived.
So what did NASA actually do? It studied two astronauts, Scott and Mark Kelly, who are also identical twins. That means they have the same DNA. They aren’t identical; no identical twins are. For example, while their DNA is identical, their fingerprints are not. The specific patterns in your fingerprints are determined by where you develop in the womb. Since identical twins cannot be in the same part of the womb, they develop different fingerprints. So first, let’s make sure we understand what is “identical” in identical twins.
A person’s DNA consists of long strings of four chemicals called nucleotide bases. Those bases are called adenine (A), thymine (T), guanine (G) and cytosine (C). The recipes for all the proteins that a person’s cells need to make are encoded in the DNA as sequences of those four bases. Just as the Betty Crocker Cook Book could be reduced to a series of dots and dashes using Morse Code, the recipes for every protein a body needs to make can be reduced to a series of four nucleotide bases (A, T, C, and G) using the genetic code. A gene, then, is simply a recipe. It tells the cell how to make a specific protein.
In identical twins, the sequences of bases in their DNA are the same. That means the recipes for all the proteins their cells make are the same. In other words, identical twins have identical genes. However, DNA is more than just a recipe book. It is a recipe book with its own instruction manual. It not only tells the cells how to make the proteins they need, but it also tells the cells how often to make those proteins. Sometimes, a cell needs to make a lot of a protein. At other times, it doesn’t need to make much of that same protein. The rate at which a gene is used to make a protein is called gene expression.
Now we can discuss what NASA did. They took advantage of the fact that they had two astronauts who are identical twins. They sent one (Scott) to the International Space Station for a full year. Most of the time, astronauts spend about six months on the station, but NASA specifically wanted to see what a longer stay would do to an astronaut. After Scott returned from his one-year mission, NASA compared his DNA to his identical twin’s DNA.
Unlike the articles I linked above lead you to believe, there was no change in the genes themselves. The sequence of nucleotide bases (and therefore the proteins his cells make) did not change compared to his identical twin. However, what did change was the instructions on how to use those genes. Some genes were used less often; some genes were used more often.
There was also one structural change to Scott’s DNA. Each chromosome has an end cap called a telomere. As far as we can tell, telomeres don’t affect the proteins made by a person’s DNA. They simply protect the genes from getting cut down during the times when DNA is duplicated for cellular reproduction. Scott’s telomeres actually elongated in space. This is interesting, because on average, telomeres tend to shorten as a person ages.
The telomere lengthening was unexpected, but the other changes weren’t. After all, we know that DNA is designed to regulate itself in response to changing conditions. How many proteins we make depends on what we are doing and how our environment is affecting us. Obviously, living in the International Space Station presents challenges to the body that living on earth doesn’t present, so it only makes sense that life on the International Space Station would affect how often Scott’s body made certain proteins.
Now here’s the interesting part: 93% of all the changes in gene expression reverted back to normal after six months. Even the telomeres shortened back to normal. However, 7% of his genes still have different rates of expression, even after six months back on earth. Remember, the changes in gene expression were expected, because of the changes in Scott’s environment and the changes in his body’s needs. However, after six months back on earth, his body has had plenty of time to adapt back to life on earth. Thus, one would expect all of the space-induced changes to have been eliminated. However, a small fraction of the gene expression is still not back to what it would have been had he never left the earth!
So unlike The Telegraph says, Scott and Mark are still identical twins. Their genes have not changed. In the same way, Newsweek is dead wrong when it says that this study indicates that space can produce long-term changes in genes. Instead, Scott now uses 7% of the same genes his twin has at different rates from his twin, even after being back on earth for six months. That’s the really interesting part of the story. This seems to indicate that long-term space missions can produce long-term changes in gene expression!
As interesting as this is, it also proves physics is the superior field: Our experiments sending someone’s identical twin into space are way cooler.
The first time I read your post, I was a little confused: it didn’t seem like you explained what exactly the molecular changes are that cause gene expression to change, and I was left with the impression that the only way one detects that DNA’s “instructions” change is by measuring bodily concentrations of proteins. So I looked at a few of the NASA links; I’m still a little confused, but when you say that DNA “is a recipe book with its own instruction manual,” what is it about the DNA that changes when the “instruction manual” changes? Do you mean methylation?
And since I’m on the topic: I should have commented earlier, but I really liked your post on Fisher’s theorem. Finally biology I can understand!
Good question, Jake. They sequenced the DNA of both twins before, several times during, and several times after. That means they looked at the full sequence of A, T, C, and G in the genome. They found several differences between the two, but that was before Scott went into space. Mutations accumulate over time in every person’s genome, so it is expected that they would have different mutations. They didn’t report any sequence differences for Scott after his time in space. Their main results come from studying the RNA in Scott’s white blood cells. As you might recall from high school biology, in order to use DNA, the cell makes a copy of it using RNA, and that RNA leaves the nucleus and goes to a ribosome in the cell. That RNA is called a “transcript” of the section of DNA being used, and the sum total of all such RNAs is called the “transcriptome.” The number of RNAs for each gene tells you the activity of the gene – the more RNAs for a gene that you find, the more active the gene is. So the main result is simply that Scott had different gene activity compared to his twin, because his transcriptome was significantly different from his twin’s.
Now…why is there different gene activity? We aren’t exactly sure. As you mention, methylation is one way that gene activity is controlled. Adding a methyl group (-CH3) to a gene can alter its activity, so it is thought that this is a fundamental way in which genes are regulated. NASA did study the methylation, but so far, the results are hard to understand. Methylation decreased during flight but returned to normal after a while on the ground. Both twins had variations in their levels of methylation during all phases of the study, but Scott had larger variations than his twin. Thus, methylation is clearly part of the reason gene expression changed. However, the methylation seems to be back to normal for Scott, but 7% of his genes are still experiencing different levels of expression.
There are other modes by which gene expression is regulated. For example, DNA is wound around proteins called histones in the nucleus. The shape of the histones affects the shape of the DNA, which in turn affects how easily it can be unwound so that RNA can make a copy. Several studies indicate that histones get modified to change the shape of the DNA and alter how fast genes can be copied. That, of course, changes the rate at which the gene is expressed. The problem is that it is much easier to measure changes in gene expression than it is to find out how that expression was actually changed.
I am glad you liked the Fisher’s theorem post. It is always good for a theory to be made into a model, because it is a good test of the theory. It seems that evolution has failed at least that particular test.
Ah, you’re right: we measure what we know how to get at – and that affects how we talk about what we’re doing. This is a good answer; thanks.
It will be interesting to see what happens if they test again in another 6 months. Will the difference decrease? Does it take more than 6 months to recover from a 12 month space flight?
Hello Dr.Wile I’m glad you have been posting again your posts help me get more information about topics that I’ve wondered about! I have a question for you lately I’ve been scared of death and I was wondering if you had any proof of the afterlife, I’m still working on becoming a faithful Christian and I am worried about it . Thanks for taking time out of your day to read this and God bless you.
Hi Evan,
The email address you gave the blog is invalid, so I can’t send you an email. I wouldn’t normally approve this kind of comment, since I like to keep the discussion related to the article. I am happy to discuss this further via email, but I will not continue the discussion on this thread, since it is not related to the article that was posted. Also, I hesitate to approve comments that have invalid email addresses.
There is only one person who has died and come back to life: Jesus. There is a lot of evidence for this, so we should probably take His word for what awaits us after death. He tells us that there is an afterlife, so in my mind, there is a lot of evidence that an afterlife exists.