Genes are no different from individuals. Sometimes they behave in a simple, logical way. Other times, they are unpredictable and influenced by their surroundings. The central dogma (DNA to RNA to protein) describes a sequential two-step process that is very similar to the linear progression from school to college and then to work. But sometimes, things get in the way that might delay our journey from school to work or might take us off course altogether! Similarly, genes can also be influenced by intangible “external” factors. The science of epigenetics studies how the expression of genes can be influenced by factors other than changes in the DNA sequence itself.
One of the many “epi” factors that modulate gene expressions, without actually changing the original nucleotide sequence, include changes in chromosomal structures. Histones, which are proteins that keep DNA tightly wound and compact, function as one such important factor for inducing an epigenetic change. When histones firmly wrap DNA, gene expression is prevented. But the addition of acetyl groups to histones results in DNA unfolding, thereby allowing gene expression. In this way, even without modifying a gene sequence, its expression can be altered by the chemical state of its histones.
Over the past years epigenetics has contributed extensively to our understanding of cancer genetics and many complex neurological disorders. Recently, scientists wondered if epigenetics played any role in a globally prevalent, multifarious enigma commonly known as “falling in love!” In a recent paper published in Nature Neuroscience, scientists explored epigenetic changes in the brains of prairie voles – animals that are well-known for their monogamous pair-bonding. Voles mate for life, share nesting and parental responsibilities, and are typically aggressive toward intruders. This unique behavior makes voles an interesting animal model in studying exclusivity, monogamy, and partner preference in humans.
Prairie vole couples that are committed to monogamy express higher levels of vasopressin and oxytocin, the social bonding neurotransmitters, but it was unclear why this was the case. Suspecting the role of epigenetics in this phenomenon, the research team studied vole couples in different conditions. Some vole couples were housed long enough for them to mate and form pair-bonds, while others were housed for only 6 hours and could not mate. The voles in this second group were injected with a drug called trichostatin A (TSA) into the nucleus accumbens – the brain’s core for reward and pleasure. Because TSA is a histone deacetylase inhibitor, the researchers speculated that, upon its injection, the resulting histone acetylation and increased gene expression would affect partner preference in the prairie voles. And, in fact, this was true. The voles that received the histone-modifying drug formed exclusive pair-bonds even though they only interacted for 6 hours and weren’t allowed to mate! Moreover, it was found that the genes for vasopressin and oxytocin receptors had been transcribed in the nucleus accumbens of these voles. Thus, a permanent genetic change was brought about by an epigenetic factor.
This study was the first to demonstrate that epigenetics can play a role in long-term behavior, like choosing life partners and forming a lifelong bond. Maybe now we can stop looking for love in all the wrong places and let our genes decide for us!
Wang H., Duclot F., Liu Y., Wang Z. & Kabbaj M. (2013). Histone deacetylase inhibitors facilitate partner preference formation in female prairie voles, Nature Neuroscience, DOI: 10.1038/nn.3420