Margaret McCarthy, PhD, professor and chairman of the Department of Pharmacology at the University of Maryland School of Medicine, recently led a new research project that studied brain development in newborn rats. A paper outlining the results of this research project was published in the latest issue of the journal Nature Neuroscience. Evaluating rat brains, McCarthy and associates discovered that giving a testosterone derivative known as estradiol, triggers a mechanism by which some specific genes in the brain are "unsilenced." The process of unsilencing these genes allows 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. Part 3 tomorrow.