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WEDNESDAY, March 31 (HealthDayNews) -- The "rat race" is over: A consortium of scientists announced Wednesday they have completed a draft copy of the genome of the Norwegian brown rat, long indispensable for research into human disease.

Analysis of the completed rat genome will be "one of the most compelling ways to understand how our own genome works," said Dr. Francis Collins, director of the National Human Genome Research Institute. He believes research into the rat's DNA map will "shine a bright light, identifying areas of important functional elements" crucial to a better understanding of disease.

The announcement that scientists had completed a draft sequence (90 percent) of the rat genome was made at a press conference in Washington, D.C.

Science achieved one of the holy grails of research in February 2001, with the completion of the draft sequence of the human genome. That achievement was followed by the December 2002 announcement that the genetic blueprint of the mouse had been similarly mapped.

The rat, long important to research, now joins that list. While rats have long been reviled as a nuisance and disease-carriers, Collins pointed out that "over the past two centuries, they have, in fact, saved countless human lives by the ways in which they have served as valuable models for medical research and drug development."

In fact, a search of the literature over the past four decades reveals that more than 900,000 studies have used the rat as their prime investigative target.

Richard Gibbs, director of Baylor College of Medicine's Human Genome Sequencing Center in Houston, is the lead author of the study detailing the rat genome, which is published in the April 1 issue of Nature.

Speaking to reporters at Wednesday's conference, he described the rat genome as "slightly smaller than the human [genome], perhaps a little larger than the mouse."

While scientists found no specific "rat" gene, they did discover that certain sequences of DNA were repeated throughout the rodent's genome -- genes specific to the rat's superior sense of smell, its improved ability to fight environmental toxins, and other characteristics "that explain the specifics of rat biology," according to Gibbs. However, on the whole, the rat genome looks remarkably like that of humans, and almost all genes known to be linked to human disease are found in the rat as well.

Gibbs also pointed out that the addition of a third mammalian genome gives researchers much more power to determine just how and when human evolution branched off from that of rodents, since all three share a common genetic ancestor in the far distant past.

"You can get this kind of timing now with a third species that you couldn't get with two," Gibbs explained, "and you may infer now the full evolutionary tree."

But it's the rat genome's potential for boosting drug research that has researchers most excited.

"Rats remain the dominant preclinical model for developing new drugs," said Howard Jacob, a study co-author and director of the Human and Molecular Genetics Center at the Medical College of Wisconsin. "Better rat models would decrease drug failures in clinical trials, which currently stand at 90 percent," he explained.

In this way, improved lab rat models should speed research, "decreasing [drug] development costs and time to market," he added.

Research based on rat genetics is already yielding results. Jacobs pointed to the example of a condition called polycystic kidney disease. Scientists investigating the illness had trouble locating the responsible gene in humans. Trying a different tack, they hit upon a gene that produced a similar disease in lab rats -- which led them to the human gene.

"Lo and behold," Jacobs said, "the same gene that causes polycystic disease in the rat causes polycystic disease in the human."

Although the draft sequencing of the rat genome covers only 90 percent of the rat's genetic makeup, scientists are confident they have mapped the vast majority of the rodent's most important genetic material. The effort, which cost more than $118 million, was a joint effort of government agencies like the Human Genome Research Institute and the National Heart, Lung and Blood Institute, academic institutions, such as the Baylor Center, and the private-sector genomic research company Celera.

Unlike the heated race to complete the human genome -- where Celera and the Human Genome Research Institute fought a highly publicized battle to reach the finish line -- efforts toward the rat genome were much less contentious, Collins said.

Baylor and Celera achieved "a wonderful partnership," he said. "There was no 'rat race' here, there was a 'rat pack.'"

Collins believes even more genome discoveries await.

"While today may be the day of the rat, tomorrow may bring publications on the chimp, the dog, and a long list of others that you can anticipate will greatly illuminate human biology, and lead us to advances in human medicine," he said.

More information

More details on the completed rat genome and its importance to medicine are available at the National Human Genome Research Institute. What's the big deal about genetic research? Go to the Baylor College of Medicine to find out.

(SOURCES: March 31, 2004, news conference with Francis Collins, M.D., Ph.D., director, National Human Genome Research Institute, Washington, D.C.; Richard Gibbs, Ph.D., Human Genome Sequencing Center, Baylor College of Medicine, Houston; Howard Jacob, Ph.D., professor of physiology and human and molecular genetics and director, Human and Molecular Genetics Center, Medical College of Wisconsin, Milwaukee; April 1, 2004, Nature)

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