As most people know, the basic component that determines how an organism develops is its genome — the complete DNA sequence that can be decoded into proteins, which ultimately make up the organism.
However, what often gets overlooked in basic biology classes is that an organism’s DNA sequence is only the first step in determining what proteins are coded. There are a myriad of ways to regulate the genome, which allows each cell to specify what it needs at a particular time to maximize its resources in an efficient manner. The study of these regulations, called epigenetics, can be passed on from generation to generation.
One specific epigenetic modification of DNA that has been known for quite some time is methylation. The methyl group, which consists of a carbon and three connected hydrogens, can be covalently bonded to certain nucleotides on a DNA sequence, leading to different levels of expression. Methylation can occur throughout the genome and leads to patterns that can be inherited, allowing progeny to inherit the same levels of gene expression as their parents.
So where is all this talk about genes and regulation going?
Well, behavioral biologists recently took to studying the development of bees, an effective model organism due to their highly structured lifestyles, which require strict behaviors from all members of the hive.
Led by Andy Feinberg, director of the Center for Epigenetics at the Johns Hopkins Institute for Basic Biomedical Sciences, a group of researchers wanted to discover if there could be a link between epigenetic modifications at the molecular level and behavioral modifications at the organismal level.
The team began their work by looking at the structure of a bee colony and studying the differences in development between types of worker bees. Studying worker bees is incredibly beneficial because they are all identical sisters with the same genomes, thus allowing researchers to pinpoint any changes in behavior with a high likelihood of correlating with changes in the genome.
Worker bees typically differentiate into two types: foragers who leave the hive for food and nurses who remain in the hive caring for the queen and her eggs. However, because both types of workers actually have the same genome, Feinberg pointed out that genes alone cannot account for their differences.
For that answer, researchers sequenced the genomes of brain DNA from 21 groups of forager bees and 21 groups of nurse bees, and took note of DNA methylation patterns. What they found was a difference in methylation at 155 regions.
To determine whether these patterns were permanent, they began toying with colony populations.
In wild bee colonies, the ratio of foragers to nurses stays at a consistent level in order to maintain the hive and the colony with the proper amount of nutrients and caretakers. So, if a colony has too few foragers, some nurses will become foragers, and vice versa.
With this in mind, Feinberg and his team took their bee colonies and started removing nurses, forcing some of the foragers to turn into nurses. After giving the colonies several weeks to adjust, the scientists then re-sequenced the genomes of the bees which had undergone the forager-to-nurse switch. What they found was 107 regions of methylation pattern difference compared with the foragers. Furthermore, 57 of those regions had been identified as differences in the original 155 regions from the previous test.
Feinberg concluded that these 57 regions were most likely the key regions of gene expression which could alter bee behavior based on whether they were methylated. In the future, the group hopes to use their findings in order to better understand behavior in humans, tying an individual’s genome with their behavioral qualities.