Epigenetics is changing the way scientists look at genetic inheritance
How does a mother’s
weight-loss surgery affect her child’s risk of obesity? It’s a question
scientists have been struggling with since a Laval University study published in April,
which looked at children born to mothers who’d undergone gastric bypass
surgery prior to their pregnancy. Researchers knew the children were
less prone to obesity, but as they tried to figure out why, they found
something unexpected. The children’s genes were different — not their
genetic code itself, but the markers in between that code. It was a
small study, but the results were striking: more than 5,000 genes were
expressed differently when parents had undergone the surgery. The
surgery had changed something in the mother’s DNA, and when the children
were born just a few years later, it appeared to have changed in them
too.
Passed from parent to child without ever touching the genetic code
The finding is part of a raft
of studies looking at the phenomenon of epigenetic inheritance — how
characteristics can be passed down from parent to child without ever
touching the genetic code. Together, these studies are having a profound
impact on how scientists look at biological inheritance and pointing
the way towards new ways of thinking about our bodies, particularly for
inherited factors like obesity or cancer risk. Instead of DNA's coded
string of nucleotides (all those Gs, Ts, As and Cs you learned in
school), this new kind of inheritance deals with methyl markers found
between the nucleotides. Those markers change the way your body’s RNA
reads the code, altering the proteins that come out of it. More
importantly, the markers can be added and removed in response to
external stimuli, making them a kind of running commentary in the
margins of your DNA.
The events of your life leave a lasting mark on your biological makeup
The science behind this
mechanism has been building steam for decades, but while we know certain
experiences or drugs can add or remove markers, scientists are still
learning how fluid the markers are. More recently, a growing number of
researchers believe they're passed from parent to child as part of DNA
transfer. On the face of it, it's a simple idea — why would the markers
on DNA behave any differently from DNA itself? — but the implications
could be enormous, rewriting century-old assumptions about the nature of
biological inheritance. In this new paradigm, the events of your life
leave a lasting mark on your biological makeup, changing not just your
own life but the lives of your descendants. In the other direction, your
own methyl markers work as a kind of ancestral memory, encoding
experiences that reach back centuries and change within each lifetime.
Instead of a permanent code, what if your body's data is written in
pencil?
Lab rats conditioned to fear a smell will pass that fear onto their children
In practice, that has led to some surprising results, even beyond stories of transgenerational weight loss. A study from Emory
this month found that lab rats conditioned to fear a certain smell will
pass that fear on to their children. The shock? The inheritance happens
biologically, even without behavioral contact. If the father runs from a
certain smell, his pups will too, even if they don't know why. Human
beings have exhibited similar behavior in earlier studies: children of
PTSD sufferers, for instance, have been shown to have lower levels of
stress-response hormones, possibly as a result of their parents’ trauma.
But these experiments could always be explained away as more nurture
than nature, the behavioral effects of growing up with a traumatized
parent. Now, it's not so clear. What if those stressful experiences are
leaving epigenetic markers, passed down from parent to child?
"It's an exciting time. We're shaking up fundamental theories."
It's entirely possible. Brian
Dias, one of the researchers behind the recent mouse-fear study, thinks
the field will have a particular impact on mental health treatments.
"We're definitely going to see the field blossom with neuropsychiatric
disorders," Dias says. "Depressive symptoms and stress biology are going
to be really important." Modern treatments see depression and anxiety
disorders as neurochemical problems, but they may come to be seen as
epigenetic problems too. It’s a particularly crucial shift because your
epigenome can be rewritten. Previous studies have used pharmaceuticals
to remove methyl markers, and Dias says the next step for his research
will be using those drugs — or other interventions — to target the
effects themselves. Now that Dias has shown he can lay down fear
markers, the challenge is figuring out a process that erases them. "It
might be drugs, it might be diet, it might be exercise," he says. "We
shouldn't shy away from these broad approaches."
Part of the reason he's staying
so open is that, for the most part, we're still in the dark about what
causes the markers to change. Moshe Szyf, a McGill professor who's been
working on cancer-based epigenetics for decades, says the uncertainty is
part of what makes the field so exciting. "We still don't really
understand how experience can create these marks," Szyf says. "It's not
so easy to find out. But we understand that there are changes." And
judging by Dias' work, we're beginning to understand how to make those
changes ourselves. The work on scent and anxiety is the beginning. If
similar work on diet or maternal behavior pans out, it could be just as
revolutionary. Szyf is optimistic, even if he doesn't expect to build a
consensus for new inheritance theories overnight. "It's an exciting
time. We're shaking up fundamental theories, and that's tough to dohttp://www.theverge.com/
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