Biomedical Beat - A monthly digest of research news from NIGMS

IN THIS ISSUE . . .
June 20, 2006

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The National Institute of General Medical Sciences (NIGMS), one of the National Institutes of Health, supports all research featured in this digest. Although only the lead scientists are named, coworkers and other collaborators also contributed to the findings. To read additional news items, visit NIGMS News.

Cool Image: Gene Silencing

Courtesy of Olga Pontes and Craig Pikaard, geneticists at Washington University in St. Louis.
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Pretty in pink, the enzyme histone deacetylase (HDA6) stands out against a background of blue-tinted DNA in the nucleus of an Arabidopsis plant cell. Here, HDA6 concentrates in the nucleolus (top center), where ribosomal RNA genes reside. The enzyme, known to switch off certain genes, silences the ribosomal RNA genes from one parent while those from the other parent remain active. This chromosome-specific silencing of ribosomal RNA genes is an unusual phenomenon observed in hybrid plants. Courtesy of Olga Pontes and Craig Pikaard, geneticists at Washington University in St. Louis.

Pikaard home page

Good News for Grapefruit Juice Drinkers

Grapefruits and juice. Courtesy of Monika Adamczyk.
Caption: Grapefruits and juice. Courtesy of Monika Adamczyk.
 

Unlike other citrus juices, a single glass of grapefruit juice can alter blood levels of drugs used to treat certain conditions like high blood pressure or high cholesterol. This effect stems from an interaction between the juice and an enzyme in the intestines, which normally chews up drugs as our bodies try to absorb them. But when grapefruit juice interacts with the enzyme, more of the drug gets in the bloodstream, causing potentially undesirable and even dangerous side effects. Now, pharmacologist Paul Watkins of the University of the North Carolina at Chapel Hill School of Medicine has identified the chemical furanocoumarin as the active ingredient in grapefruit that causes this effect. The finding could lead to a juice lacking this chemical and to the identification of other food products with similar drug interactions.

Full story
Watkins lab home page
Article abstract (from the May 2006 issue of The American Journal of Clinical Nutrition)

Tracking Genetic Variation

Double helix and Etruscan funerary statue. Courtesy of Elise Belle

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Caption: Double helix and Etruscan funerary statue. Courtesy of Elise Belle.

Human population genetics research can shed light on the genetic variation between individuals and the evolutionary processes that give rise to that variation. Researchers collaborating on a population genetics project have produced a computational model of modern human evolution that can be used to test a range of hypotheses related to demographics and genetic diversity. Anthropologist Joanna Mountain of Stanford University, working with Guido Barbujani of the University of Ferrara in Italy, used the model to rule out a genetic link between contemporary Tuscans and the ancient Etruscans, a people that inhabited Tuscany centuries ago. The findings challenge the common assumption that current inhabitants of a region are descended from earlier residents and are helping scientists understand the origin of patterns of genetic variation observed today.

Full story
Mountain lab home page (no longer available)
Article abstract (from the May 23, 2006, issue of PNAS)

Making Sense of Cilia

Chlamydomonas reinhardtii, a green alga. Courtesy of DOE Joint Genome Institute.

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Caption: Chlamydomonas reinhardtii, a green alga. Courtesy of DOE Joint Genome Institute.

A simple green alga that lives in small ponds and puddles may hold secrets about human health and disease. That’s according to William Snell, a cell biologist at the University of Texas Southwestern Medical Center, who studies the microscopic hairs called cilia that help the organism move and mate. In humans, cilia play a role in the sense of smell, brain development, kidney function, and many other activities. Now, Snell has identified a biochemical process that cilia on the alga use to send signals. His work could shed light on other functions of cilia in humans, some of which remain unknown. Since defective cilia can lead to human disorders, such as kidney disease, the work also may set the stage for drug discovery.

Full story
Snell home page
Article abstract (from May 5, 2006, issue of Cell)

Neutrons Offer Insights into Proteins

A diagram of the atomic arrangement in the active site of the enzyme D-xylose isomerase. Courtesy of Bunick.

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Caption: A diagram of the atomic arrangement in the active site of the enzyme D-xylose isomerase. Courtesy of Bunick.

The same technique that can detect moisture in the wings of jet fighter planes has shown its strength in determining the shapes of proteins. A team of researchers, including structural biologist Gerard Bunick of the University of Tennessee, used neutrons to locate hydrogen atoms in the active site of D-xylose isomerase—an enzyme that serves as a model for understanding other types of proteins and as a catalyst for making commercial products, such high-fructose corn syrup and ethanol. Typically, hydrogen atoms make up about half of all the atoms in a protein and play a key role in protein function. Because other protein determination techniques, such as X-ray crystallography, do not adequately capture the location of hydrogen atoms, the neutron approach offers a complementary strategy that could speed drug discovery and improve medicines.


Fox Chase home page
Full story
Article abstract (from the May 30, 2006, issue of PNAS)