To Bee or Not to Bee: The caste system is alive and well in honeybee society. A female embryo fed on “royal jelly” emerges as a Queen, specialized to lay eggs, while other females are sterile workers. All workers begin as nurses, tending to the eggs. After a few weeks some nurses switch to become foragers leaving the hive to search for nectar. They are genetically identical, so what determines caste? The answer lies in epigenetics.
• Epigenetics is the bees knees! It is the chemical modification of DNA over and above the underlying genetic code. DNA is wrapped tightly around histone proteins, like beads on a chain. (a) Relaxed DNA has chemically modified histones (green dots). This makes it open for business, inviting transcription factors (TF) to get to work transcribing a gene. (b) DNA methyltransferase (DNMT) adds methyl groups (grey triangles) to CpG dinucleotides. (c) This triggers different chemical modifications (red) to the core histone, to condense and inactivate the DNA structure. Genes are silenced when transcription factors cannot bind to them. So, is the division of bee labor decided by these chemical tags? Not to belabor this, but in short, yes.
• Tag Teams: Johns Hopkins molecular biologist Andy Feinberg teamed up with bee expert Gro Amdam (Arizona State Univ, Tempe) to show for the first time, epigenetic changes associated with behavior. Age matched workers and foragers have 155 differences in DNA methylation, mostly associated with genes that regulate other genes. Better yet, these changes are reversible. Using hive trickery, researchers introduced foragers to a new hive. This induced about half of them to revert back to worker bees. Remarkably, DNA methylation tags reverted as well. This may help decipher complex behavioral changes in humans.
REF: Herb et al. (2012) Reversible switching between epigenetic states in honeybee behavioral subcastes. Nature Neuroscience DOI: 10.1038/nn.3218
Image: Modified from Strietholt et al. (2008) http://arthritis-research.com/content/10/5/219
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