'New Lamarcksim' - parental experience influences genetic make-up
I'm paraphrasing an article from New Scientist here for those that don't have access. Much of the phrasing comes from the original printed article, and all should be credited to Emma Young.
It seems that a growing number of scientists are finding that environmental factors can have an impact on the traits of an individual, and on the traits their offspring will inherit, without any major changes to the genetic sequence itself. This has been dubbed 'New Lamarcksim' after Jean-Baptiste Lamarck who proposed that characteristics acquired during a lifetime can be passed on to offspring.
This work centres around epigenetics. Epigenetics deals with how genes are regulated and expressed in a cell and is the basis for the formation of the different tissues in our body from cells comprising identical genetic stock. We know that genes - and possible non-codind DNA - control RNAi and are involved in determining epigenetic settings, but it is now becoming increasinly apparent that environmental factors have an impact as well. The best example of this comes from honeybees. All female honeybees develop from genetically identical larvae, but those fed on royal jelly become fertile queens while others are doomed to life as sterile workers. In March this year a team led Ryszard Maleszka showed that epigenetic mechanisms account for this. They used RNAi to silence a gene for DNA methyltransferase in honeybee larvae. Most of these larvae emerged as queens without ever having tasted royal jelly.
In 2000 a team at Duke University performed an experiment on genetically identical mice. The mice carried the agouti gene which makes them fat and prone to cancer. One group of females was given a diet rich in methyl groups before conception and during pregnancy. Their offspring were slim and lived to a "ripe old age". The same results were found with females given genistein, an oestrogen-like compound found in soya. The dose was designed to be comparable to a human on a high soya diet. The chance was associated with increased methylation of 6 DNA base-pair sites which regulate the agouti gene.
These studies indicated that the diet of a mother (and thus her natal offspring) can have a huge impact on the traits displayed by her children in later life. However, diet is not the only environmental factor that can influence traits. Michael Meaney at McGill University found that mice negelcted by their mothers are more likely to be fearful in adulthood, and that these mice show much higher levels of methylation of certain genes involved in stress response.
In humans too, there are hints that damaging experiences in early life can also affect epigenetic settings. Meaney and his colleagues reported a study of 13 men who had commited suicide, all of whom had been victims of child abuse. They showed clear epigenetic differences in their brains compared with the brains of men who had died of other causes. It is possible that these chances may have been caused by their experiences as children, and it is suggested could have attributed to their suicides as well.
Arturas Petronis, at the Centre for Addiction and Mental Health in Toronto, reported an epigenome-wide scan of brain tissue from 35 people who had suffered from schizophrenia (American Journal of Human Genetics, vol 82, p 696). He and his colleagues found a distinctive epigenetic pattern, controlling expression of roughly 40 genes. As with the suicidal men in Meaney's study, these epigenetic marks may have arisen during early development. Yet there are also hints that those with schizophrenia inherited the traits from their parents, and that they in turn might pass the marks onto their children. In theory, epigenetic marks are wiped clear between generations in mammals. The abnormalities in Petronis's subjects were not restricted to the frontal cortex: they were also present in their sperm.
In fact some papers are now suggesting that diseases such as cancer could be inherited through epigenetic changes in the mother (The New England Journal of Medicine, vol 356, p697). Paternal inheritance has also been raised by Matthew Anway. Anway and colleagues demonstrated that rats exposed to the fungicide vinclozolin while in the womb were less fertile and had a higher than normal risk of developing kidney defects (Science, vol 308, p 1466). These effects were passed from father to son through 3/4 generations. The team found no DNA changes only altered methylation patterns in the sperm. Not only that, but these males tended to be avoided by females, who appeared to be selecting on an epigenetic basis rather than a genetic one. This has reinforced the suggestion that epigenetic variation could be adaptive (the water flea daphnia, for example, develop large, defensive spines when predators are around. If they then reproduce their offspring also have the spines, even if there are no predators around).
So the diet we consume and our environment may actually have an impact on the traits we pass onto our children without requiring any change to our DNA.
Forget Jesus, the stars died so that you could be here
- Lawrence Krauss