Rat joins genetic mapping of mice and men
(Agencies)
Updated: 2004-04-01 09:36

The genetic code of the rat joined the growing list of creatures whose DNA has been mapped Wednesday and experts said it will make the laboratory rat, already beloved by scientists, an even better tool for fighting human disease.

The rat is only the third species to be sequenced to such a degree, after the completed human genome sequence in April 2003 and the draft mouse genome in December 2002.

Scientists say mice and humans descended from a common ancestor about the size of a small rat.

It confirms that the laboratory rat is in fact a good choice for medical research. Almost all human genes associated with diseases have counterparts in the rat genome, the researchers write in this week's issue of the journal Nature.

"This is an investment that is destined to yield major payoffs in the fight against human disease," Dr. Elias Zerhouni, head of the National Institutes of Health that funded most of the research, said in a statement.

"For nearly 200 years, the laboratory rat has played a valuable role in efforts to understand human biology and to develop new and better drugs," he added.

"Now, armed with this sequencing data, a new generation of researchers will be able to greatly improve the utility of rat models and thereby improve human health."

Of mice and men

The researchers, led by a team at Baylor College of Medicine's Genome Sequencing Center in Texas, chose the Brown Norway strain of laboratory rat, known scientifically as Rattus norvegicus.

This species was best known in the past for infecting ships and is distinct from the smaller black rat, Rattus rattus, notorious for spreading plague.

"As we build upon the foundation laid by the Human Genome Project, it's become clear that comparing the human genome with those of other organisms is the most powerful tool available to understand the complex genomic components involved in human health and disease," said Dr. Francis Collins, head of the National Human Genome Research Institute.

Having the rat genome along with the mouse and the human allows scientists to triangulate, just as mariners triangulate to navigate using the stars and the sun, said Baylor's Richard Gibbs, who led the study.

That in turn will help show what makes mice different from people, and rats from mice, the scientists told a news conference.

"If we have two things we can't really tell how far apart we are. Now that we have a third species we can see whether the changes are rat changes, mouse changes or human changes," Gibbs said in an interview.

The map has already shown an explosion of change in the rat's genetic makeup, Gibbs said -- helping separate the rat from other rodents and especially mice.

Rats have significant differences from mice and from people notably in olfaction and immune system genes.

But it is not so much new genes as extra copies of genes, Collins said.

"It certainly doesn't seem that any new genes were invented along the way," Collins said.

In other words, what makes us different from rats or mice is not some unique human gene, but rather what the body does with its genes.

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