New study: DNA methylation in memory specificity and relearning

Over the last years one of our aims was to characterise the role DNA methylation plays in honeybee memory formation. There is still much we don’t know, but our newest study (Biergans et al., 2016) could identify two distinct functions of DNA methylation in bees: memory specificity and relearning.

During olfactory reward learning (the assay we used here) bees learn to associate an odor with a sugar reward just like they would in the wild while foraging (Bitterman et al., 1983). Memory specificity is crucial for bees during foraging to reliably return to a good food source. DNA methylation can support memory specificity (Biergans et al., 2012). Our new study shows that this role of DNA methylation actually is context dependent: If bees receive much information during training (several odor-sugar pairings) DNA methylation supports memory specifity. If bees receive little information, however, (one odor-sugar pairing) DNA methylation suppresses memory specificity. Thus, DNA methylation might support an ecologically meaningful behavioural response depending on the environmental information bees receive (e.g. odor indentity predicts food vs. odor identity is neligible as predictor for food). Additionally, DNA methylation supports relearning of previously encoutered odors, but not learning of odor information in general.

Little is known so far about how these findings translate to mammals. DNA methylation is important during extinction in mammals, but no study to date investigated its role in memory specificity and relearning. Other epigenetic mechanisms – histone modifications – have, however, been shown to affect memory specificity after auditory fear conditioning in mammals (Bieszczad et al., 2015). Thus, epigenetic regulation of memory specificity might be conserved across animals. Further analysis of the epigenetic regulation of memory specificity and relearning is crucial in order to understand the dynamics of memory formation beyond ‘simple’ associative learning.

 

Biergans, S.D., Reinhard, J., Claudianos, C., Galizia, C.G. (2016) DNA methylation adjusts the specificity of memories depending on the learning context and promotes relearning in honeybees. Frontiers in Molecular Neuroscience 9 (82), doi: 10.3389/fnmol.2016.00082
Biergans, S.D., Jones, J.C., Treiber, N., Galizia, C.G., and Szyszka, P. (2012). DNA methylation mediates the discriminatory power of associative long-term memory in honeybees. PloS one 7 (6), e39349.
Bieszczad, K.M., Bechay, K., Rusche, J.R., Jacques, V., Kudugunti, S., Miao, W., Weinberger, N.M., McGaugh, J.L., and Wood, M.A. (2015). Histone deacetylase inhibition via RGFP966 releases the brakes on sensory cortical plasticity and the specificity of memory formation. The Journal of neuroscience : the official journal of the Society for Neuroscience 35 (38), 13124-13132.
Bitterman, M.E., Menzel, R., Fietz, A., and Schäfer, S. (1983). Classical conditioning of proboscis extension in honeybees (Apis mellifera). Journal of comparative psychology 97, 107-119.
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