She discusses research in which the DNA of rats who where raised by attentive vs inattentive mothers was examined, and it was found that the DNA of rat pups who had been nurtured was normal while the DNA of rats who had not been nurtured as pups had markers at the stress response gene that made the rats unable to handle stress throughout their lifetime. Interestingly, the next generation of pups, the babies of the non-nurtured rats, also had the DNA marker that turned off their stress response gene. Somehow the treatment that their parents had received as pups had been passed along to them in their DNA. How can this be happening?
When rat pups are nurtured, serotonin is released in their brains that triggers a "switch" on the DNA, a receptor called Lysine 4, which tells the DNA to unwrap in such a way as to "turn on" a stress response gene, allowing the pups to handle stress. One way that DNA expression is regulated, as in this case, has to do with the histones that it is wrapped around. Histones are like spools that the DNA is wrapped around and can be rolled up or unrolled to expose sections of DNA for expression. The question is, how do these histones "know" what ton do? How do they "know" the cell's conditions to know how to alter DNA expression, so that genes are expressed at just the right times and then turned back off at the right times?
Many people think that RNA, a large molecule closely related to DNA, might be the answer. RNA molecules can sense the environment and can go into the nucleus of the cell. She and her research team found that in the case of gender identity, there does seem to be an RNA molecule that is capable of communicating to histones so that they can in turn alter gene expression based on environmental cues.