Sex differences in cognition and behavior–such as increased aggression in males–are usually thought to involve hormones, which can “masculinize” or “feminize” a brain temporarily or permanently. But now, a mouse study shows that some sex-linked genes don’t need hormones to shape male and female behavior.
The Y chromosome in males have been identified to contain the gene SRY (Sex determining Region Y ) that determines the formation of testicles long back, and by early ’90s scientists had learned how to breed mice whose genes and hormones function independently. Since human SRY is similar to SRY of mice, a model of SRY function has been developed in mice.
By knocking out the testes-determining SRY gene, on the Y chromosome, researchers made XY mice that churn out estrogen; and by adding SRY to females, they produce XX mice that manufacture male hormones.
With the help of such mice, it was shown that genes unrelated to hormone production also played an independent role in aggression and nurturing behaviors. This was a new revelation because, until then it was believed that only the hormones determined such behaviours.
A team led by neuroscientist Jane Taylor of Yale University was interested in habit-forming behaviors in which gender differences also have been documented. She and her colleagues trained these mice, as well as normal male and female mice, to poke their noses through one of three holes in order to obtain a food pellet. Then, some of the mice were subjected to “conditioned taste aversion”. After eating the food, they were injected with a chemical that made them sick (something like what we use in alcoholic patients to help them quit drinking.) Ordinarily, mice will quickly learn to avoid the food, but they will still eat it if they have developed an automatic habit. That happened more often for the XX mice regardless of whether they produced male or female hormones.Thus, they say, the sex difference must have something to do with genes that are not involved in the production of sex hormones.
Neurobiologist Lawrence Cahill of the University of California, Irvine, says that the study “relates very well to established sex differences in the acquisition of addictive habits.” For example, women progress from casual drug-taking to a drug habit faster than men do–a phenomenon some have attributed to hormones. Taylor says that the work also implies that women can be good multitaskers–by quickly forming habits that leave their higher brain functions free for other chores.
Blogger’s Post Script: The last piece about the study implying that women can be good multitaskers seems to be a hasty extrapolation to me, as the quoted study doesn’t provide results of any of that sort, although estrogen has been linked to many skilled activities and greater attention span. It is also important to keep in mind that the precise mechanisms of sex differentiation are still unknown and that gender differentiation is accomplished through a cascade of gene activations. Further factors are involved, then, before as well as after the SRY expression – for example the WT-1, SF-1, DAX-1, SOX-9 genes. (I’m not being chauvinistic here – just bringing to notice a bad practice in science reporting, that’s all.)
Report in Nature Neuroscience. (21 October).
News modified from Sciencenow.