Can experiences be passed on to offspring?

New Scientist, 06 February 2009

WHAT was your mother up to before you were even a twinkle in her eye? You might not think it matters, but it seems that in mice at least, mothers that receive mental training before they become pregnant can pass on its cognitive benefits to their young.

Previous studies in both people and animals have shown that a mother's experiences while pregnant can affect her offspring's gene expression and health, even years later. However, it was not known if experiences prior to pregnancy had an effect.

Larry Feig at Tufts University School of Medicine in Boston and his colleagues bred "knockout" mice that lacked a gene called Ras-GRF-2, causing them to have a memory defect. Normally, if mice in a cage receive a shock to their feet, they freeze in fear if they are then placed back into the same cage. In contrast, Ras-GRF2 knockout mice did not associate the cage with fear.

Before they reached adolescence, the team kept these knockout mice in a cage filled with toys for two weeks. Such "enriched environments" are known to enhance learning and memory. In the knockout mice, the enriched cage was enough to compensate for their memory defect: when tested on the fear task, they associated the shock with the cage, like normal mice.

To see if this compensation could be passed on to young, the researchers waited for these enriched knockout mice to reach sexual maturity, bred them and tested their offspring on the fear task. Despite being reared by an "unenriched" knockout foster mother - to rule out the effects of spending time with a mouse they could learn directly from - the offspring associated the electric shock with the cage, just like their enriched mothers and those without the genetic defect.

In contrast, the offspring of knockout mice who did not receive the enrichment did not associate the shock with the cage (Journal of Neuroscience, DOI: 10.1523/jneurosci.5057-08.2009).

This effect was only seen in offspring whose knockout mothers had an enriched cage: having an enriched knockout father but a normal knockout mother was not enough to remedy the defect in the offspring.

As the offspring had the same genetic defect as their mothers, the researchers attribute the enhanced cognition in these mice to the time their mothers spent in the enriched cage prior to becoming pregnant.

The effect was not passed on to a third generation and was only inherited if the offspring were conceived within three months of enrichment. So the researchers suspect that the mother passes on this cognitive effect during gestation, perhaps by releasing hormones that prompt "epigenetic" chemical markers to appear on her unborn child's genes, regulating their expression after birth.

Moshe Szyf at McGill University in Montreal, Canada, calls the work "remarkable". "The mother can modulate the intellectual capacity of her young," he says. "If it happens in humans it has immense implications." But he wishes Feig had pinned down exactly how the cognitive effects are inherited. "It smells like epigenetics, but there's no proof."