Friday, December 31, 2010

BRAIN GENE A TRIGGER FOR DETERMINING GENDER

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University of Adelaide researchers are a step closer to unraveling the mysteries of human sexual development, following genetic studies that show male mice can be created without a Y chromosome – through the activation of an ancient brain gene.

Males usually have one Y chromosome and one X chromosome, while females have two X chromosomes. A single gene on the Y, called SRY, triggers testes development in the early embryo, and once these begin to form, the rest of the embryo also becomes male.

However, Adelaide researchers have discovered a way of creating a male mouse without a Y chromosome by activating a single gene, called SOX3, in the developing fetus. SOX3 is known to be important for brain development but has not previously been shown to be capable of triggering the male pathway.

In a major international collaborative study, they also have shown for the first time that changes in the human version of the same gene are present in some patients with disorders of sexual development.

The results of this work are published online today in the Journal of Clinical Investigation, and will be published in the journal's print version in January 2011.

"The Y chromosome contains a gene called SRY that functions as a genetic switch to activate the male pathway during embryonic development," says Associate Professor Paul Thomas from the University of Adelaide's School of Molecular & Biomedical Science.

"The SRY genetic switch is unique to mammals and is thought to have evolved from the SOX3 gene during early mammalian evolution."

Associate Professor Thomas and his colleagues have generated male mice with two X chromosomes by artificially activating the SOX3 gene in the developing gonads.

"These XX male 'sex reversed' mice are completely male in appearance, reproductive structures and behavior, but are sterile due to an inability to produce sperm," he says.

"We have suspected for a long time that SOX3 is the evolutionary precursor gene for SRY. By showing that SOX3 can activate the male pathway in the same way as SRY, we now believe this to be true."

This work is a longstanding collaboration between Associate Professor Thomas and Dr Robin Lovell-Badge at the Medical Research Council National Institute for Medical Research in London, who discovered the SRY gene in mice more than 20 years ago.

Dr Lovell-Badge says he's excited about the findings: "SOX3 normally functions in the development of the nervous system, but it is now clear that a mutation that makes it active in the early gonad can turn it into the switch that makes testes develop.

"It is now very likely that something similar to what has happened in the XX male mice and humans we describe also occurred in our early mammalian ancestors, and this led to the evolution not only of SRY, but of the X and Y chromosomes. Just think of all the trouble this little gene has caused!" he says.

Further collaborative research with Professor Andrew Sinclair at the Murdoch Children's Research Institute in Melbourne and Professor Eric Vilain at UCLA (University of California Los Angeles) has also shown that changes in the human SOX3 gene are present in some individuals who are XX males.

"From a genetic perspective, cases of XX male sex reversal are particularly intriguing and are poorly understood," Associate Professor Thomas says.

"This discovery provides new insight into the genetic causes of disorders of sexual development, which are relatively common in the community.

"For the future, this discovery will impact on the molecular diagnosis of these disorders and, ultimately, help us to develop therapies or technologies to improve clinical outcomes," he says.

(Photo: Sandra Piltz)

University of Adelaide

PLACEBOS WORK -- EVEN WITHOUT DECEPTION

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For most of us, the "placebo effect" is synonymous with the power of positive thinking; it works because you believe you're taking a real drug. But a new study rattles this assumption.

Researchers at Harvard Medical School's Osher Research Center and Beth Israel Deaconess Medical Center (BIDMC) have found that placebos work even when administered without the seemingly requisite deception.

The study published on December 22 in PLoS ONE.

Placebos—or dummy pills—are typically used in clinical trials as controls for potential new medications. Even though they contain no active ingredients, patients often respond to them. In fact, data on placebos is so compelling that many American physicians (one study estimates 50 percent) secretly give placebos to unsuspecting patients.

Because such "deception" is ethically questionable, HMS associate professor of medicine Ted Kaptchuk teamed up with colleagues at BIDMC to explore whether or not the power of placebos can be harnessed honestly and respectfully.

To do this, 80 patients suffering from irritable bowel syndrome (IBS) were divided into two groups: one group, the controls, received no treatment, while the other group received a regimen of placebos—honestly described as "like sugar pills"—which they were instructed to take twice daily.

"Not only did we make it absolutely clear that these pills had no active ingredient and were made from inert substances, but we actually had 'placebo' printed on the bottle," says Kaptchuk. "We told the patients that they didn't have to even believe in the placebo effect. Just take the pills."

For a three-week period, the patients were monitored. By the end of the trial, nearly twice as many patients treated with the placebo reported adequate symptom relief as compared to the control group (59 percent vs. 35 percent). Also, on other outcome measures, patients taking the placebo doubled their rates of improvement to a degree roughly equivalent to the effects of the most powerful IBS medications.

"I didn't think it would work," says senior author Anthony Lembo, HMS associate professor of medicine at BIDMC and an expert on IBS. "I felt awkward asking patients to literally take a placebo. But to my surprise, it seemed to work for many of them."

The authors caution that this study is small and limited in scope and simply opens the door to the notion that placebos are effective even for the fully informed patient—a hypothesis that will need to be confirmed in larger trials.

"Nevertheless," says Kaptchuk, "these findings suggest that rather than mere positive thinking, there may be significant benefit to the very performance of medical ritual. I'm excited about studying this further. Placebo may work even if patients know it is a placebo."

Public Library of Science (PLoS)

PSYCHOLOGISTS FIND SKILL IN RECOGNIZING FACES PEAKS AFTER AGE 30

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Scientists have made the surprising discovery that our ability to recognize and remember faces peaks at age 30 to 34, about a decade later than most of our other mental abilities.

Researchers Laura T. Germine and Ken Nakayama of Harvard University and Bradley Duchaine of Dartmouth College will present their work in a forthcoming issue of the journal Cognition.

While prior evidence had suggested that face recognition might be slow to mature, Germine says few scientists had suspected that it might continue building for so many years into adulthood. She says the late-blooming nature of face recognition may simply be a case of practice making perfect.

"We all look at faces, and practice face-watching, all the time," says Germine, a Ph.D. student in psychology at Harvard. "It may be that the parts of the brain we use to recognize faces require this extended period of tuning in early adulthood to help us learn and remember a wide variety of different faces."

Germine, Duchaine, and Nakayama used the web-based Cambridge Face Memory Test -- available at www.testmybrain.org -- to test recognition of computer-generated faces among some 44,000 volunteers ages 10 to 70. They found that skill at other mental tasks, such as remembering names, maxes out at age 23 to 24, consistent with previous research.

But on a face-recognition task, skill rose sharply from age 10 to 20, then continued increasing more slowly throughout the 20s, reaching a peak of 83 percent correct responses in the cohort ages 30 to 34.

A follow-up experiment involving computer-generated children's faces found a similar result, with the best face recognition seen among individuals in their early 30s. After this, skill in recognizing faces declined slowly, with the ability of 65-year-olds roughly matching that of 16-year-olds.

"Research on cognition has tended to focus on development, to age 20, and aging, after age 55," Germine says. "Our work shows that the 35 years in between, previously thought to be fairly static, may in fact be more dynamic than many scientists had expected."

(Laura Germine.) (Photo: Stephanie Mitchell)

Harvard University

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