Fri, Sep 12, 2014 - Page 9 News List

Generation game: Understanding the epigenetic lottery

Research on mice claims to show that environmental factors have an impact not just on individuals, but on their offspring too

By Angela Saini  /  The Observer

Illustration: Mountain People

As with so much in science, this story owes a lot to mice. The tale begins with a pregnant mouse in a laboratory in Boston, Massachusetts. Such is the unfortunate lot of a lab rodent that she was kept on a near-starvation diet when she was close to giving birth. As scientists expected, her babies were born smaller than usual. When they were raised normally, they later developed diabetes.

Now comes the twist. Even though these mice were fed well, their own young were also born unusually small and with a higher risk of diabetes. This was strange, because nothing had changed genetically and they had not suffered any problems in the womb or after they were born. They should have been perfectly healthy.

This puzzling study, published last month, echoes many performed on mice, worms and plants in the past few years in the name of a relatively young branch of science called epigenetics. In seeking to answer that eternal question of nature versus nurture — Does our upbringing shape us or do our genes? — this field has radically introduced a mysterious third element into the mix: the life experience of previous generations.

There are many definitions of epigenetics, but simply put, it is a change in our genetic activity without changing our genetic code, University College London and the University of Bristol geneticist Marcus Pembrey says.

It is a process that happens throughout our lives and is normal to development. Chemical tags get attached to our genetic code, like bookmarks in the pages of a book, signaling to our bodies which genes to ignore and which to use, he added.

For decades, people have thought of our offspring as blank slates. Now, epigeneticists are asking whether in fact our environment, from smoking and diet to pollution and war, can leave “epigenetic marks” on our DNA that could get passed on to subsequent generations. They call the phenomenon epigenetic inheritance.

Until recently, most scientists assumed that whatever epigenetic marks we accrued during our lives were erased in our children. Embryos are known to be reprogrammed in the womb.

“For something to be transmitted epigenetically from one generation to the next, it would have to resist this reprogramming,” says Anne Ferguson-Smith, a geneticist at the University of Cambridge who ran the pregnant mouse study with her colleagues in Boston.

The notion that infants may retain some parental baggage has enormous repercussions for child development and evolution. Parents could suddenly find themselves responsible for passing on not only their poor genes, but also their poor lifestyles. Also, instead of adapting to our environments slowly over many generations, humans may be doing it much, much faster. Some have even breathlessly suggested that Charles Darwin’s theories will need to be rewritten.

However, before you throw out your biology textbooks, Ferguson-Smith counters that transgenerational epigenetic experiments are difficult to perform and can be misinterpreted.

“Journals are very excited about this. They want to publish this stuff, but we must be more cautious,” she says.

The basic problem is that researchers, including herself, still do not understand the scientific mechanism behind epigenetic inheritance, which would explain exactly how it happens.

Azim Surani, a leading developmental biologist and geneticist at the University of Cambridge, adds that while there is good evidence that epigenetic inheritance happens in plants and worms, mammals have very different biology. Surani’s lab carried out thorough studies on how epigenetic information was erased in developing mouse embryos and found that “surprisingly little gets through” the reprogramming process.

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