Scientists Create Genetically Modified 'marathon Mice'

WASHINGTON, Aug 23 (AFP) - Scientists have discovered a genetic tweak that turns mice into marathoners, but is not likely to be ready for use in humans by for the 2008 Olympics, according to a study released Monday.
The endurance of the genetically engineered mice grew more than the untreated mice. And the mighty mice did not become obese during periods of inactivity and when fed high-fat diets, because the genetic change acted like physical exercise.
"Two groups have genetically engineered different pathways that change mice from Sunday morning joggers to Olympic marathoners," according to a statement from the Public Library of Science Biology, an Internet scientific magazine.
Some of the genetic modifications "not only enhance physical performance but could presumably protect against obesity," said Ronald Evans, of Salk Institute in San Diego, California.
"The finding that endurance and running capacity can be genetically manipulated suggests that muscle tissue is far more adaptable than previously thought. Maybe Olympiads can be made after all -- but don't give up on training just yet," he said.
Evans, who headed the investigation, said that the modified mice ran twice as fast and twice as far than their unmodified cousins, nearly 1,800 meters (1,970 yards) compared with 900 meters (985 yards). The genetically engineered mice ran an hour longer than the normal mice.
His team succeeded in modifying the mice through a gene that is activated only when the mouse is submitted to endurance training. Once activated, the gene prompts an increase in physical capacity among normally idle mice and raises their ability to burn fats, even without physical activity.
The researchers determined which muscle tissues are the fast-twitch muscle fibers, known as type II, used for sprinting and the slow-twitch muscles, type I, needed for endurance.
There are no known side-effects for the mice, who are nine months old. The researchers want to know more, mostly if the genetic modification reduces the mice's life expectancy.
There is a gap to bridge between genetic modifications possible in mice and their application to human beings. However, Evans has already gotten the attention of large pharmaceutical laboratories with his genetic work in stimulating the production of so-called good cholesterol, which is being tested in humans.