Switching roles within the hive is reflected in reversible epigenetic changes.
Subtle differences in the DNA of honeybees are reflected in the bees' roles within the hive. These DNA modifications are normally fixed, but research published today in Nature Neuroscience1 reveals the first example of reversible changes to DNA associated with behaviour.
All honeybees (Apis mellifera) are born equal, but this situation doesn’t last long. Although genetically identical, the bees soon take on the specific roles of queen or worker. These roles are defined not just by behavioural differences, but by physical ones. Underlying them are minor modifications to their DNA: ‘epigenetic’ changes that leave the DNA sequence intact, but that add chemical tags in the form of methyl (CH3) molecules to sections of the DNA. This in turn alters the way a gene is expressed2.
Once a bee is a queen or worker, they fulfil that role for life — the change is irreversible. But that is not the case for the subdivisions among the workers. The workers start out as nurses, which look after and feed the queen and larvae, and most then go on to become foragers, which travel out from the hive in search of pollen. Again the two types have very different methylation patterns in their DNA.
This time, however, as the latest results show, the DNA modifications are reversible: if a forager reverts to being a nurse, its methylation pattern reverts too.
Led by Andrew Feinberg of Johns Hopkins University in Baltimore, Maryland, and Gro Amdam of Arizona State University in Tempe, the researchers coaxed forager bees back into nursing roles by removing all the nurses from the hive while the foragers were out looking for pollen. When the foragers returned, they noticed the lack of nurses, and about half of them took on nursing roles. Examination of the methylation patterns in DNA from their brain cells showed that these too had switched back to the pattern associated with nurses.
“What is exciting is that the genes that change back are the same genes that changed in the other direction initially — and the same ones that would regulate epigenetic behaviour,” says Feinberg.
Gene Robinson, a bee researcher at the University of Illinois at Urbana-Champaign, who was not involved in the research, says that although the paper does not necessarily prove that epigenetic mechanisms cause behavioural differences, “it demonstrates for the first time that if behaviour is reversible so is the methylation”.
But Amdam says that the fact that honeybees can revert to a previous role indicates that there is a kind of ‘epigenetic roadmap’. “Brain cells can rely on shifts between these roadmaps to control different behaviours correctly,” she says.
A greater understanding of how epigenetics affects behaviour may lead to insights into human biology, Feinberg says, noting that epigenetic effects on human behaviour might express themselves in addiction, learning and memory. If the link between behaviour and methylation patterns “is true in a bee, it is likely to also be true in us”, he says.
This does not mean that artificially changing the methylation pattern of DNA would result in a desired behaviour, but “it would be great if that was feasible”, says Amdam. “Reversing possible ‘bad’ epigenetic marks in human physical and psychological diseases is already a big research interest in biomedicine. Perhaps bees can be used to figure out how it could be done.”
Herb, B. R. et al. Nature Neurosci. http://dx.doi.org/10.1038/nn.3218 (2012).
Lyko, F. et al. PLoS Biol. 8, e1000506 (2010).
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Phenotypic plasticity and the epigenetics of human disease 2007-May-23
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Guttridge, N. Job swapping makes its mark on honeybee DNA. Nature (2012). https://doi.org/10.1038/nature.2012.11418