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How does environment influence our genes? How are modifications made to our genome without actually altering the DNA sequence? That’s the study of epigenetics. Epigeneticists can study cancer and other disease through this lens, and also gain insights to behavior.
One way gene expression is altered through epigenetics is called DNA methylation. These are chemical tags that can regulate how genes function. Ed Yong puts it this way in his Discover blog:
These marks, known as methyl groups, are like Post-It notes that dictate how a piece of text should be read, without altering the actual words.
Epigeneticist Andy Feinberg, of John Hopkins, wanted to understand how DNA methylation might be identified in changes in behavior so he teamed up with Gro Amdam, of Arizona State University, a bee behavior expert.
Honeybees make excellent study subjects for this purpose because they are social creatures with very compartmentalized behavior. Female bees are either queens or worker bees, and once the path is chosen, there’s no turning back.
Within the worker bees, however, there are behavior distinctions that are a bit more transient. Workers begin as nurses—tending to the larvae. After two to three weeks, they become foragers, leaving the hive to gather pollen.
The researchers decided to study the chemical tags, DNA methylation, of the two groups—nurses and foragers. “Genes themselves weren't going to tell us what is responsible for the two types of behavior,” Feinberg says. “But epigenetics—and how it controls genes—could.”
Analyzing the patterns of DNA methylation in the brains of 21 nurses and 21 foragers, the team found 155 regions of DNA that had different tag patterns in the two types of bees. The genes associated with the methylation differences were mostly regulatory genes known to affect the status of other genes.
Then the scientists got tricky. They removed some of the nurses from the hive. When this happens in nature, some of the foragers are able to revert to nursing to fill the gap. Sure enough, the same thing happened in Feinberg’s and Amdam’s experiment—several of the foragers went back to being nurses.
This time, 107 DNA regions showed different tags between the foragers and the reverted nurses, suggesting that the epigenetic marks were not permanent but reversible and connected to the bees’ behavior and the facts of life in the hive.
“It’s like one of those pictures that portray two different images depending on your angle of view,” Amdam says. “The bee genome contains images of both nurses and foragers. The tags on the DNA give the brain its coordinates so that it knows what kind of behavior to project.”
The researchers say they hope their results may begin to shed light on complex behavioral issues in humans, such as learning, memory, stress response and mood disorders, which all involve interactions between genetic and epigenetic components similar to those in the study.
The study is published this week in Nature Neuroscience.
Image: Louise Docker/Wikipedia