The fascinating memory of a honeybee could give us hints about our own long-term memory formation, scientists suggest. According to a new study, epigenetic marks are added to the DNA of honeybees in a response to an enzyme known as DNA methyltransferase (Dmnt) and removed in response to a Dnmt inhibitor drug. This epigenetic mechanism may play a role in memory specificity and influence the removal and re-acquisition of memory.
When human memory breaks down or fails, disorders such as dementia and Alzheimer’s can arise. The simple brain of a honey bee may offer us clues to the processes underlying long-term memory formation, specifically the epigenetic mechanism known as DNA methylation.
Dr. Stephanie Biergans, the study’s first author from the University of Queensland, Australia, said, “We show that DNA methylation is one molecular mechanism that regulates memory specificity and re-learning, and through which experiences of the organism could be accumulated and integrated over their lifetime.”
Honeybees have an exceptional ability to learn and remember. By learning patterns and landmarks, they can orient themselves and even communicate to others the location of food sources. They are able to remember and share with members of their colony the direction and distance to flowers through what is known as the waggle dance.
“They are social insects that interact, teach and learn, making them successful foragers. Bees remember how to find a food source, how good the source was, and how to return to the hive,” explained Dr. Biergans.
Just as dogs can give us epigenetic clues about our own wellbeing, honeybees can teach us about our own complex memories – how they might be formed and extinguished over time. Honeybees’ simpler brains and much smaller genome make them an ideal model for studying various long-term memory processes. Previous researchers have also found that numerous honeybee genes are more similar to genes of invertebrates than other insects, many which are linked to circadian rhythms, DNA methylation, and learning and memory.
Memory is a complex process, a mystery humans continue to try to solve. Scientists know that molecular changes, which then lead to physical changes involving neural connections, occur in the brain as a result of memory formation. Epigenetic mechanisms such as DNA methylation or histone modification have been thought to influence memory formation by impacting gene expression without altering the genes themselves.
“We knew that DNA methylation is an epigenetic process that occurs in the brain and is related to memory formation,” Biergans said. “When we block this process in honeybees it affects how they remember.”
The bees were taught by the research group to anticipate sugar when a smell was presented to them. This learning method is best known as classical conditioning. One group learned this association over a period of time, whereas the other group was presented with the sugar and smell in combination just once. Then, the research team used a compound that inhibits DNA methylation, known as a DNA methyltransferase inhibitor. Memory formation between both groups was compared and tested with and without DNA methylation. They also found that DNA methylation impacts a bee’s relearning, particularly when they paired the sugar with a different scent.
“When the bees were presented with sugar and a smell many times together, the presence of DNA methylation increased memory specificity — they were less responsive to a novel odour. On the other hand, when only introduced to the combination once, DNA methylation decreased specificity,” Biergans concluded.
Once a bee gets good quality pollen from a flower, it will come to associate that flower’s scent with high quality nourishment and stick to that flower or seek out that type over others. This process, which involves the formation of memories, helps reveal clues to our own brain and memory.
“By understanding how changes to the epi-genome accumulate, manifest and influence brain function, we may, in the future, be able to develop treatments for brain diseases that also develop over a lifetime,” Biergans hopes. “There is thought to be a genetic predisposition for some conditions, such as Alzheimer’s and dementia, but in many cases environmental factors determine whether the disease will manifest.”
Source: Biergans, S.D., Claudianos, C., Reinhard, J., Galizia, C.G. DNA Methylation Adjusts the Specificity of Memories Depending on the Learning Context and Promotes Relearning in Honeybees. Frontiers in Molecular Neuroscience, 9:82.
Reference: Jensen, A. R. Honeybee memories: another piece of the Alzheimer’s puzzle? Frontiers Blog. 12 Dec 2016. Web.