Epigenetic changes don’t last

First comprehensive inventory of epigenetic changes over several generations shows that these often do not last and therefore probably have limited effects on long-term evolution

Jean-Baptiste Lamarck would have been delighted: geneticists no longer dismiss out of hand his belief that acquired traits can be passed on to offspring. When Darwin published his book on evolution, Lamarck’s theory of transformation went onto the ash heap of history. But in the last decade, we have learned that the environment can after all leave traces in the genomes of animals and plants, in form of so-called epigenetic modifications. Scientists at the Max Planck Institute of Developmental Biology in Germany have now produced the first comprehensive inventory of spontaneous epigenetic changes. Using Arabidopsis, the workhorse of modern plant genetics, the researchers determined how often and where in the genome epigenetic modifications occur – and how often they disappear again. They found that epigenetic changes are many orders of magnitude more frequent than conventional DNA mutations, but also often short lived. They are therefore probably much less important for long-term evolution than previously thought.

More important than the state of individual cytosines is probably the methylation of larger segments of the genome. “In each plant we found only about 30 such regions in which they differed from the other lines,” explains Becker. Hagmann adds: “Such whole-sale epigenetic changes appear to be as rare as true DNA sequence mutations”. These differences can nevertheless appear very rapidly. The biologists discovered one region that first lost its methyl groups, only to become completely remethylated in the next generation.

What makes epigenetics interesting for human health is the fact that some epigenetic changes can be triggered by external factors. There is evidence that nutrition or the bond between children and their parents can leave traces in the genome that can be passed on to the next generation. The limited stability of DNA methylation implies, however, that such differences do not necessarily last forever, which is probably not a bad idea because a famine might not last forever. It also means that altered DNA methylation often cannot become subject to natural selection.

The results of the Max Planck scientists demonstrate that epigenetic differences can also arise spontaneously, without drastic changes in the environment. After all, the growth conditions in the green house, where each of the 10 lines was propagated, were constant. This opens the door to further speculation. “We suspect that the epimutation increase is higher and more variable when plants grow in nature, where they are stressed all the time”, says Becker. If this were paralleled by an even higher reversion rate, then the importance of epigenetics for long-term evolution would be even lower.

Participating scientists and institutions
Detlef Weigel, Claude Becker, Jörg Hagmann, Jonas Müller and Daniel Koenig in the Department of Molecular Biology at the Max Planck Institute for Developmental Biology, Germany; Oliver Stegle and Karsten Borgwardt from the Machine Learning and Computational Biology Research Group at the Max Planck Institutes for Developmental Biology and Intelligent Systems, Germany.