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Monday, June 29, 2009

Transgenerational persistence of epigenetics

A new open access study highlights that epigenetic changes can persist through many generations. While the researched worked with plants, the situation is surely very much the same with animals and humans.

F. Johannes et al., Assessing the Impact of Transgenerational Epigenetic Variation on Complex Traits. PLoS Genetics, 2009.

Loss or gain of DNA methylation can affect gene expression and is sometimes transmitted across generations. Such epigenetic alterations are thus a possible source of heritable phenotypic variation in the absence of DNA sequence change. However, attempts to assess the prevalence of stable epigenetic variation in natural and experimental populations and to quantify its impact on complex traits have been hampered by the confounding effects of DNA sequence polymorphisms. To overcome this problem as much as possible, two parents with little DNA sequence differences, but contrasting DNA methylation profiles, were used to derive a panel of epigenetic Recombinant Inbred Lines (epiRILs) in the reference plant Arabidopsis thaliana. The epiRILs showed variation and high heritability for flowering time and plant height (~30%), as well as stable inheritance of multiple parental DNA methylation variants (epialleles) over at least eight generations. These findings provide a first rationale to identify epiallelic variants that contribute to heritable variation in complex traits using linkage or association studies. More generally, the demonstration that numerous epialleles across the genome can be stable over many generations in the absence of selection or extensive DNA sequence variation highlights the need to integrate epigenetic information into population genetics studies.

Not all is hardcoded in the genome, the program can be and is in fact altered by "softer" means, means that have nevertheless certain transgenerational persistence. This way the phenotype is changed without need for the genome to mutate. Non-genetic variants appear around a basic genic core, increasing variability and potentially adaptability in the short run too.


Manjunat said...

I think Epigenetics is an exception and can be safely ignored. Another sensational "Neanderthal introgression" concept.

Maju said...

Well, I would not be surprised if it affected some of our most plastic inheritance too. For example, someone mentioned elsewhere that Germans have rapidly evolved from mostly brachicephalic to mostly dolicocephalic in just 70 years (since 1940). This can't be attributed to a genetic change but could have been affected by epigenetic changes maybe promoted by food or whatever other reason.

Ebizur said...

In the case of Germany, some information on regional demography may be crucial for the correct interpretation of these CI figures.

In the first half of the twentieth century, at least, the average CI of the northern half of Germany was dolichocephalic, and the average CI of the southern half of Germany was, like other areas in and around the Alps, brachycephalic. If the northern half of Germany had a greater total population, then the average CI of Germany as a whole might be dolichocephalic even while the south of the country maintained its previously noted tendency toward brachycephaly. It may also be a simple matter of where in Germany the majority of the sample has been obtained. I would rather attribute such a rapid "change" in the reported CI of Germans to demography and sampling bias rather than to an epigenetic phantom.

Maju said...

I really don't know the details but intergenerational changes in cranial shape have been reported in other circumstances and helped to reduce the prestige of anthropometry in general. That's why I wonder if epigenetics may have something to do with that.

I cannot find the original comment at Dienekes (rather recent) that mentioned that. The author noted that the difference was brutal of 8 or maybe 12 CI points (from memory), so I suspect that a mere sample bias can hardly be the reason.