In September researchers from China and France announced they had managed to clone rats, adding it to the growing list of animal species that have been successfully cloned.
Figuring out how to clone the rat took considerably longer than the mouse (which was cloned in 1998) due in part to the speed with which rat embryos develop — the eggs would start to develop before researchers could swap genetic material to produce the clone.
French researchers solved that problem by using an inhibitor to delay the development of the fertilized rat egg long enough to insert the clone DNA material.
Rats are used in a number of animal models where they are closer analogues to human physiology than mice (such as diabetes for one), and the ability to clone rats and make gene knockout rats will greatly aid research into a variety of human ailments.
Sources:
Rat Clone Is New Big Cheese of the Lab. Los Angeles Times, September 26, 2003.
Rat is latest clone. The BBC, September 25, 2003.