One of the most fascinating things about epigenetics is the implication it has for inheritance and evolution. Theories and hypotheses are everywhere, of course, but until Sir Richard Branson launches a Virgin Time Travel business, actually measuring the changes from thousands of years of natural selection will remain a pretty tall order. Two recent papers from Australian scientists though have come up with some clever ways to find the new data they need to understand environmental epigenetics, inheritance and evolution.
In the first paper, (PLoS One, January 2012) Dr. Catherine Suter from the Victor Chang Cardiac Research Institute and her collaborators obtained the first single-base resolution DNA methylation profile of an ancient mammalian genome. The team used bisulphite allelic sequencing of loci in samples form Bison priscus remains (we all have those laying around in the back of our freezers, right?), which roamed the earth back in the late Pleistocene. Surprisingly, (to us at least) they found that the differentially methylated regions of imprinted loci had matching methylation patterns to fresh bovine samples.
Aside from showing that the methylomes of ancient Bison are pretty similar to modern cows, their findings also proved the stability of methylated cytosines over long periods of time and show the first direct evidence that methylation patterns can be studied in the DNA from ancient specimens. So perhaps you don’t really need a time machine to study evolution as long as you do have a time capsule, like the Bison samples.
In a newly released second study, Suter and colleagues studied several generations of genetically identical mice with an epiallele susceptible to methyl donors. The researchers found that with dietary supplements of methyl donors, the phenotype of this epiallele changed and that trait was passed on, and even became more prevalent in subsequent generations, as long as selection and the supplementation remained in effect. Once the dietary supplement and selective pressure was removed, the phenotypic changes remained for only a single generation before reverting back to their original state.
This work is the first demonstration that selection for epigenetic traits can have cumulative, heritable effects in mammals and suggests an alternative to the notion that natural selection acts on genetic variation alone. Suter and her crew think this mechanism might be a way that species can rapidly adapt to new environmental conditions, like a change in available diet, and then even change back a few generations later if needed.
Find the full report, time-travel not needed, at Proceedings of the Royal Society B: Biological Sciences, February 2012.