DNA scientists hail victory in rat race

By STEVE CONNOR



Scientists have decoded the full DNA sequence of the laboratory rat, a breakthrough they believe will revolutionise the investigation of the human genes behind serious illnesses such as cancer.

The international research consortium which carried out the study said it would enable the brown rat's genes to be compared directly with those of the two other species of mammals to be deciphered - man and mouse.

Analysing the genes of mice and rats would allow scientists to gain a fuller understanding of the complexities of the human genome, said Francis Collins, director of the US National Human Genome Research Institute in Washington.

"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," Dr Collins said.

It has been almost 200 years since the brown rat, Rattus norvegicus, was first used by scientists to understand human physiology and medicine and since then the rodent has become almost a byword for laboratory experimentation.

The "book" of the rat genome is about 2.75 billion letters long, making it slightly smaller than that of humans, which consists of 2.9 billion letters, but bigger than the mouse genome, at 2.6 billion letters.

Most of the rat's genes are shared with humans, allowing researchers to investigate how a gene works in people by studying the role and defects of the same gene in the laboratory animal.

The scientists, whose study is published in the journal Nature, said that the rat genome would help to develop new treatments for a range of medical problems, notably cancer, diabetes, psychiatric disorders such as addiction and nerve degeneration.

Professor John Mullins of the University of Edinburgh said that knowing the genome of the rat would help medical researchers find new treatments for diseases of the heart and circulatory system, one of Britain's biggest killers.

"This is really exciting news for research into heart disease, stroke and high blood pressure. Rats are integral to the study of cardiovascular disease, and sequencing of the rat genome will help us to identify genes that are important to these illnesses," Professor Mullins said.

Although rats, mice and humans share most of their genes, there are some, notably those involved in the sense of smell and in detoxifying the body, that appear to be unique to the rat.

The researchers found that among the 30,000 or so genes of the rat, there are hundreds of extra olfactory genes involved with the sense of smell, which plays a role in the rodent's reproductive behaviour.

Ian Jackson of the Medical Research Council's Human Genetics Unit in Edinburgh, said that rats were far more important than mice for studying behaviour and psychology.

"Rats are used a lot in studies of the genetics of behaviour and psychology and in some respects they are better than mice in behavioural tests - they seem to be smarter," Dr Jackson said.

"The rat genome sequence should be a great help in tracking down genes that affect behaviour," he said.

Dr Collins said rats had significant differences from mice and from people notably in olfaction and immune system genes.

But it was not so much new genes as extra copies of genes, he 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.

TOOLS AGAINST DISEASE

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

Most of the rat's genes are shared with humans, allowing researchers to investigate how a gene works in man by studying the role and defects of the same gene in the laboratory animal.

- INDEPENDENT