Generally speaking, most animal species show some form of sexual dimorphism. This difference in physiology usually reflects different tasks that gender in a species needs to perform. For example, many birds have the males to court females, so the males have colorful patterning. Similarly, the brains of animals also generally show a difference in physiology between genders. It depends on the species of course, but often some slight difference between the size and connections of different brain regions is found.
Like many physiological features, these differences manifest during gestation (for mammals anyways). A group from the University of Maryland wanted to find out exactly how such changes were regulated. (via ScienceDaily) Their first experiments involves giving developing mice a derivative of testosterone. They found that this unsilence certain genes that are associated with masculinization.
In this case, the unsilencing was done through enzymes called DNA methyltransferases. These enzymes are a key component of epigenetics, a.k.a. gene regulation. Many mechanisms within the cell rely on modifying proteins or other structures through the adding or removing of small molecules. Methylation is one of these, and can affect DNA directly or proteins associated with its packaging.
Either way, interfering with this class of enzymes seems to be the key contributor to sexual dimorphism in the brain. Despite these features being established during embryonic development, the researchers were able to modify them after birth. Injecting an inhibitor of DNA methyltransferase one weeks after birth, transformed a target region of the brain.
They decided to target a region called the preoptic area, which among other things plays a substantial role in male sexual behavior. Not only did female mice given this inhibitor have a masculine looking physiology in that brain region, but they behaved differently as well. In fact they behaved like male mice, when it came to the mating and sexual behavior.
As a follow-up experiment, mice were also produced without the genes for these enzymes at all. They similarly showed masculine features in the brain, both in physiology and behavior, among females. Both experiments confirm the role of DNA methylation in the development of sexual dimorphism. The first experiment is the first hint that such development is flexible, even after an animal is born.
However, these experiments are only preliminary. The group plans to conduct more research on this area of brain development. They've also been doing interesting work on how the immune system plays a role in all of this, and that may be a focus of future work.
