Wednesday, January 17, 2007

The Sins of Our Grandmothers

From: New Scientist, Nov. 13, 2006


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

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

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

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)