The Norway brown rat joins humans and mice as the third mammal to have its entire genetic code unveiled. An international group of scientists has published the draft genome sequence of Rattus norvegicus, in the journal Nature. For years, medical researchers have used the rat in laboratory studies to understand disease and develop new treatments, so its entire DNA sequence should prove invaluable. And comparing the rat genome to the human and mouse genomes will allow scientists to work out which DNA sequences are unique to rodents, and which are shared by all mammals. 'This is an investment that is destined to yield major pay-offs in the fight against human disease', said Elias Zerhouni, director of the US National Institutes of Health (NIH).
The work was carried out by the Rat Genome Sequencing Project Consortium (RGSPC), made up of 220 researchers based at private and public institutions in six different countries. As well as the rat genome itself, which consists of 2.75 billion base-pairs (chemical 'letters') of DNA, the RGSPC publication also includes a detailed comparison of the rat, mouse and human genomes. It reveals that humans and rodents last shared a common ancestor around 80 million years ago, with rats and mice parting company 12-24 million years ago. Around ten per cent of the rat's genes are shared by mice, but absent from humans, suggesting they are 'rodent-specific'. Rats also have several genes not shared by either humans or mice, most of which are involved in detecting smells and dealing with poisons.
The rat genome contains an estimated 25,000 different genes, 90 per cent of which have human counterparts. Professor John Mullins, a geneticist at Edinburgh University said of the publication: 'This is really exciting news for research into heart disease, stroke and high blood pressure', adding that the 'sequencing of the rat genome will help us to identify genes that are important to these illnesses'. Researchers looking at diabetes, psychiatric disorders and cancer will also benefit from a detailed knowledge of rat genes. Several other mammal genomes are in the pipeline - for example, a draft version of the chimp genome was unveiled at the end of last year, with a detailed analysis to be published shortly.
The cow, rhesus macaque monkey, opossum and boxer dog genomes are also nearing completion; these should shed further light on human genes. '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 Francis Collins, director of the US National Human Genome Research Institute.