Are you a jealous, devious high-school student who wishes to clamber up the social pecking order and claim your spot as the queen bee of the school? Well, scientists have discovered a way that worker bumblebees rise to the top of bee hierarchy and become queens, but the key does not lie in wearing the hottest fashions, giving out free food, or crafting duplicitous ways to make your frenemies mysteriously disappear. The key lies in epigenetics.
We went over epigenetics in Unit 7 – epigenetics is heritable changes in gene expression that occur without any alteration to DNA sequences. Two of the forms of epigenetics that we learned about were DNA methylation and histone acetylation. In DNA methylation, chemical markers called methyl groups are added to DNA, which decreases the rate of transcription of the targeted genes. During histone acetylation, acetyl groups are added to histones, loosening the tightly wound structure of DNA and thus promoting gene transcription.
Researchers have discovered that when a queen bee goes missing from the hive or gets too old, worker females rise up in revolt, becoming more aggressive and even laying their own eggs due to the development of their ovaries. The researchers at the University of Leicester in England discovered methylation differences between the genomes of queen-less reproductive workers and queen-less non-reproductive workers. Thus the researchers observed that a shortage of methyl groups on DNA was associated with more aggressive, reproducing worker bees.
The scientists then attempted to determine whether the increased aggressiveness and overall change in behavior in the worker bees was solely caused by changes in patterns of genomic methylation. The researchers used decitabine, a drug that is used to treat acute myeloid leukemia and inhibits the enzyme that attaches methyl groups to DNA. When leaderless worker bees received decitabine in their nectar, they became more aggressive and thus more likely to develop ovaries and lay eggs. Hence, the results suggested that changes to the methylation patterns in the DNA of bumblebees directly correlates to a change in their behavior and affects their role in the hive.
Some entomologists at the University of Leicester suspect that something deeper might be at play. Genomic imprinting is a phenomenon in which specific genes are turned on based on what parent they were inherited from. Scientists know that genomic imprinting occurs in humans – an example is Angelman’s Syndrome – but there is not any direct evidence that genomic imprinting occurs in bumblebees. Scientists believe that genomic imprinting may play a role in the observed methylation pattern effects because methylation is an epigenetic tag for genomic imprinting – genomic imprinting often involves DNA methylation. However, scientists need to identify specific genes that meet certain criteria and then perform a series of testcrosses to determine whether genomic imprinting is occurring in bumblebees.
Though genomic imprinting cannot be confirmed until the full genome of a bumblebee is available, Gene Robinson (a geneticist at the University of Illinois at Urbana-Champaign) says that this study “represents an important first step.” Future investigations can shed more light on the role that epigenetics and genomic imprinting have on social behavior and what makes a worker bee reach queenly prominence.