Nav: Home

Researchers unravel mechanism that plays key role in sexual differentiation of brain

March 31, 2015

During prenatal development, the brains of most animals, including humans, develop specifically male or female characteristics. In most species, some portions of male and female brains are a different size, and may have a different number of neurons and synapses. However, scientists have known little about the details of how this differentiation occurs. Now, a new study by researchers at the University of Maryland School of Medicine (UM SOM) has illuminated details about this process.

Margaret McCarthy, PhD, professor and chairman of the Department of Pharmacology, studied brain development in newborn rats. She found that giving estradiol, a testosterone derivative, triggers a mechanism by which certain genes in the brain are "unsilenced," allowing them to initiate the process of masculinization. This process involves a group of enzymes known as DNA methyltransferases, or Dnmts, which modify DNA to repress gene expression.

The paper was published in the latest issue of the journal Nature Neuroscience.

"Nobody has ever shown that this is how the process works," said Prof. McCarthy. She collaborated with Bridget Nugent, PhD, who is now a researcher at the University of Pennsylvania. "This gives us a new understanding of how gender is determined in the brain.

Prof. McCarthy and Nugent also found that inhibiting Dnmts has powerful effects, even outside the usual window of development. During prenatal development there is a restricted time frame during which the brain takes on male or female characteristics. Scientists had thought that once this window closed, it could not be reopened. But the two researchers found otherwise. They succeeded in transforming the brain of a female rat after the window had closed, giving it the characteristics of a male rat brain.

Prof. McCarthy and Nugent injected Dnmt inhibitors into a specific region of the female brains, a region known as the preoptic area, or POA. In every species that's been studied, including humans, the POA plays a key role in governing male sexual behavior. The injections occurred after the first week of birth, the time when the window for brain sexual differentiation was thought to have been closed. Despite this, the preoptic area in these animals was transformed, and took on structural characteristics of a male rat. The female rats also behaved differently, displaying sexual behavior typical of male rats. In another experiment, they genetically deleted the Dnmt gene in female mice; these animals also showed male behavior patterns.

"Physically, these animals were females, but in their reproductive behavior, they were males," said Nugent. "It was fascinating to see this transformation."

Prof. McCarthy has focused much of her work on the neuroscience of sex differences. In previous research she found sex and gender differences in levels of a protein associated with language acquisition and development. This finding may be associated with higher levels of communication among females in some species.

Intriguingly, the latest study also found that inflammatory immune cells known as microglia appear to play a role in masculinization, in part through their production of prostaglandins, a neurochemical normally associated with illness. In recent years, scientists have increasingly realized that the immune system is integral to the development of the brain; Prof. McCarthy and her group are the first to show that it is also important for establishment of sex differences in the brain. The current discovery is another piece in that puzzle; they showed that Dnmt enzymes control expression of genes that play a role in inflammation and immunity, and also in the sexual differentiation of the brain. Prof. McCarthy is now doing additional research on the links between the immune system and brain sex differences.

"Prof. McCarthy's work provides new insight into brain development and gender," said Dean E. Albert Reece, MD, PhD, MBA, who is also the vice president for Medical Affairs, University of Maryland, and the John Z. and Akiko K. Bowers Distinguished Professor and Dean of the School of Medicine. "She has spent years working on this area, and this is just the latest discovery in her impressive career."
-end-
About the University of Maryland School of Medicine

The University of Maryland School of Medicine was chartered in 1807 and is the first public medical school in the United States and continues today as an innovative leader in accelerating innovation and discovery in medicine. The School of Medicine is the founding school of the University of Maryland and is an integral part of the 11-campus University System of Maryland. Located on the University of Maryland's Baltimore campus, the School of Medicine works closely with the University of Maryland Medical Center and Medical System to provide a research-intensive, academic and clinically based education. With 43 academic departments, centers and institutes and a faculty of more than 3,000 physicians and research scientists plus more than $400 million in extramural funding, the School is regarded as one of the leading biomedical research institutions in the U.S. with top-tier faculty and programs in cancer, brain science, surgery and transplantation, trauma and emergency medicine, vaccine development and human genomics, among other centers of excellence. The School is not only concerned with the health of the citizens of Maryland and the nation, but also has a global presence, with research and treatment facilities in more than 35 countries around the world.

medschool.umaryland.edu/

University of Maryland School of Medicine

Related Immune System Articles:

The immune system may explain skepticism towards immigrants
There is a strong correlation between our fear of infection and our skepticism towards immigrants.
New insights on how pathogens escape the immune system
The bacterium Salmonella enterica causes gastroenteritis in humans and is one of the leading causes of food-borne infectious diseases.
Understanding how HIV evades the immune system
Monash University (Australia) and Cardiff University (UK) researchers have come a step further in understanding how the human immunodeficiency virus (HIV) evades the immune system.
Carbs during workouts help immune system recovery
Eating carbohydrates during intense exercise helps to minimise exercise-induced immune disturbances and can aid the body's recovery, QUT research has found.
A new model for activation of the immune system
By studying a large protein (the C1 protein) with X-rays and electron microscopy, researchers from Aarhus University in Denmark have established a new model for how an important part of the innate immune system is activated.
More Immune System News and Immune System Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#534 Bacteria are Coming for Your OJ
What makes breakfast, breakfast? Well, according to every movie and TV show we've ever seen, a big glass of orange juice is basically required. But our morning grapefruit might be in danger. Why? Citrus greening, a bacteria carried by a bug, has infected 90% of the citrus groves in Florida. It's coming for your OJ. We'll talk with University of Maryland plant virologist Anne Simon about ways to stop the citrus killer, and with science writer and journalist Maryn McKenna about why throwing antibiotics at the problem is probably not the solution. Related links: A Review of the Citrus Greening...