Rats join the roster of clones.

After a long struggle, researchers have finally cloned the rat, a longtime laboratory favorite used to study high blood pressure, diabetes, brain diseases, and many other human illnesses. The accomplishment sets the stage for the creation of genetically engineered rats that can serve as models for many more human diseases.

Would-be rat cloners had become frustrated because unfertilized rat eggs typically begin dividing within an hour of their removal from a female's oviduct. That didn't allow enough time to pull off the pivotal initial step of cloning: removing an egg's DNA and transferring in DNA from the cell of another animal.

Biologists from the National Institute of Agronomy Research (INRA) and the biotech company genOway, both in Lyon, France, treated the eggs with a compound that blocks an enzyme involved in their initial divisions. Once the new DNA was added, however, the eggs began to divide. This strategy enabled the successful cloning of fertile and seemingly healthy rats, INRA's Qi Zhou and his colleagues report in the Sept. 25 Science.

Researchers should be able to genetically design rats by manipulating DNA in lab-grown rat cells before it's transferred to an emptied egg and to produce a clone.--J.T.