New Scientist, November 13, 2006
YOU ARE WHAT YOUR GRANDMOTHER ATE
[Rachel's introduction: The field of study called epigenetics keeps coming up with unpleasant surprises -- new ways that environmental conditions today can harm our children and grandchildren tomorrow.]
By Roxanne Khamsi
A mother's diet can change the behaviour of a specific gene for at least two subsequent generations, a new study demonstrates for the first time.
Feeding mice an enriched diet during pregnancy silenced a gene for light fur in their pups. And even though these pups ate a standard, un-enriched diet, the gene remained less active in their subsequent offspring.
The findings could help explain the curious results from recent studies of human populations -- including one showing that the grandchildren of well-fed Swedes had a greater risk of diabetes.
The new mouse experiment lends support to the idea that we inherit not only our genes from our parents, but also a set of instructions that tell the genes when to become active. These instructions appear to be passed on through "epigenetic" changes to DNA -- genes can be activated or silenced according to the chemical groups that are added onto them. Gene silencer
David Martin at the Children's Hospital Oakland Research Institute in California, US, and colleagues used a special strain of genetically identical mice with an overactive version of a gene that influences fur colour. Mice with the AVY version of this gene generally have golden fur.
Half of the mice were given a diet enriched with nutrients such as vitamin B12 and zinc. These nutrients are known to increase the availability of the "methyl" chemical groups that are responsible for silencing genes. The rest of the mice received a standard diet.
The pups of mice on the standard diet generally had golden fur. But a high proportion of those born to mice on the enriched diet had dark brown fur.
Martin believes that the nutrient-rich maternal diet caused silencing of the pups' AVY genes while they developed in the womb. Passed down
Intriguingly, even though all of the pups in this generation received a standard diet, those that had exposure to a high-nutrient diet while in the womb, later gave birth to dark-coated offspring. Their control counterparts, by comparison, produced offspring with golden fur.
This shows that environmental factors -- such as an enriched diet -- can affect the activity of the AVY gene for at least two generations, the researchers say.
"The results make it clear that a nutritional status can affect not only that individual, but that individual's children as well," says study member Kenneth Beckman. Skin colour
Beckman notes that the AVY gene is linked to weight and diabetes risk. He adds that there is some evidence that a related gene in humans might affect skin colour -- but it is unknown if it also affects weight.
Even though humans may have a similar gene, they should not make dietary changes based on the results of the mouse experiment, researchers stress. "It would be irresponsible to make any prescriptions about human behaviour based on these findings," says Martin.
An earlier Swedish study which used historical data of harvests in Sweden, found that a youngster had a quadrupled risk of diabetes if their grandfather had good access to food during his own boyhood.
Journal reference: Proceedings of the National Academy of Science (DOI: 10.1073/pnas.0607090103)