Limiting calories extends life of yeast

Removal of certain genes combined with reduction in calorie intake could increase lifespan, new research on baker's yeast finds. In two separate studies, both led by Valter D. Longo of the University of Southern California, researchers have increased the lifespan of yeast by using a combination of dietary and genetic modifications. In one study, the researchers genetically modified baker's yeast by removing two genes responsible for aging and related diseases like cancer, and restricted the yeast's calorie intake. Reduction in calorie intake has been known to increase lifespan by about two- to threefold in yeast. In the mutated yeast, however, the lifespan increased by almost tenfold. In another study, the researchers decided to see if deletion of the genes alone, without restricting calorie intake, increased lifespan. They found that mutated yeast cells lived five times longer. The aging-related genes studied by Longo's group are found in all organisms from yeast to humans, suggesting it may someday be possible to make a drug to prevent aging-related diseases in humans.

BOTTOM LINE: "Certain genetic modifications can arrest the aging process," said Longo. CAUTIONS: The is the first study to test effects of mutations plus calorie restriction and more work is needed to understand this relationship and extrapolate the results to humans. WHAT'S NEXT: Longo's group is studying lifespan increase in mice and in a human population in Ecuador that naturally lacks these aging-related genes. WHERE TO FIND IT: PLOS Genetics, Jan. 25, and Cell Biology, Jan. 14. SENA GOPAL DESAI

Bye-bye, black sheep? British researchers have found that the numbers of black sheep in wild herds native to St. Kilda, Scotland, have been dwindling due to a genetic quirk that delivers dark coloring - along with a shortened lifespan. This combination of sequences appears to be a package deal for sheep: They inherit the dark coat color and low fitness traits together. The sequences, called alleles, which code for these particular versions of the coat-color and fitness traits, are found in neighboring locations on the sheep chromosome. This means that the genetic chances of unlinking the alleles naturally are very slim, and black sheep are likely doomed over the long-run. Dark sheep have roamed the island of Soay on the St. Kilda archipelago for more than 4,000 years. Only in the past 95 years have light-colored sheep mysteriously appeared in Soay and begun to thrive more than the dark ones. Scientists have considered such "genetic hitchhiking" - where advantageous or disadvantageous traits like life expectancy get linked to neutral ones, such as wool color - as quite rare, according to Christopher Schneider, associate professor of biology at Boston University, who was not involved in the research. "But the Soay sheep study shows that hitchhiking can be an important evolutionary process."

BOTTOM LINE: The black sheep of Scotland are likely dying out, though it's unclear what this means for humans who consider themselves the black sheep of their family. CAUTIONS: Jacob Gratten, a principal investigator in the study at the University of Sheffield, notes that the demise of black sheep is a wild phenomenon - breeders and farmers won't be affected. WHAT'S NEXT: The researchers are investigating the evolutionary origin of the light color mutation. WHERE TO FIND IT: Science, Jan. 17 GRACE TIAO