Modified Genes Linked To Behavior

DNA methylation ensures the right genes are expressed in the right cell so that nose hair genes don’t get turned on in the pancreas, for example. Now the epigenetic mark has been shown to also correlate with the behavior of honeybee nurses and foragers.

For the first time, researchers have associated patterns of DNA methylation in an organism with reversible behavior—in the case of honeybees, the ability of nurses to switch to foragers and then back to nurses, explains Andrew P. Feinberg, an epigenetics researcher at Johns Hopkins University. Feinberg made the discovery in collaboration with Arizona State University bee biologist Gro V. Amdam (Nat. Neurosci., DOI: 10.1038/nn.3218).

Bees living in a hive are nearly identical in terms of genetics, Feinberg says, but the behaviors of bee castes (queen, nurse, forager, and worker) are remarkably different and have long made researchers suspect an epigenetic role in behavior.

Nurse bees that have just emerged from cocoons feed and clean bee larvae. When older, the nurse bees are able to turn into forager bees, which discover nectar and signal to worker bees the location of these food supplies, Feinberg says.

The research team found that otherwise genetically identical nurse and forager bees have different methylation patterns in 155 genes found in their brain cells, suggesting that the patterns dictate behavior. To prove this hypothesis, the team used “a strategy of hive trickery” by removing all the nurse bees while the foragers were away, the paper notes. When the foragers returned to the nurse-free hive, many reverted to a nursing role. The team found that after this role reversal, the methylation patterns in 57 genes from the former foragers had changed to correspond to nurse patterns.

Scientists have long proposed that epigenetics affects behavior, comments Chuan He, who studies DNA methylation at the University of Chicago. “The most interesting part is that this effect is reversible. Reverting foragers back to nurses reestablishes methylation patterns.”

The team found no difference in the DNA methylation patterns of the brains of hive queens and hive workers, whose destinies of laying eggs and ferrying pollen are sealed early in life. Feinberg argues, however, that the irreversible fates of queens and workers may be controlled at the heterochromatin level, where larger sections of the genome are silenced.