Since 1981, scientists had thought that genetically engineered rats would follow quickly after the development of the technique in mice. They have been able for a long time to modify the DNA in mouse embryonic stem cells and to create mice not only with altered genes, but also with missing or added ones.

However, the techniques scientists used with mice didn’t work with rats, whose dimensions can make them better models as humans and rats are physiologically very alike and medical study of rats can better apply to individuals, compared to medical studies of the other rodents. Besides, humans and rats tend to respond in a similar way to drugs. However, the cost of keeping lab rats is approximately 10 times higher than for mice.

Now, researchers discovered a formula that allows them to capture and maintain indefinitely the basic embryonic stem cells of a mammal, including pigs, cows and rats. Researchers at USC consider deriving embryonic stem (ES) cells from rats a breakthrough that will allow experts to create more successful animal models for the study of several human diseases.

According to Qilong Ying, a native of China and the study's principal investigator "this is a major development in stem cell research because we know that rats are much more closely related to humans than mice in many aspects of biology.”

The discovery was made in labs at the University of Edinburgh and the University of Southern California (USC), Los Angeles and was published in the Dec. 26 issue of the scientific journal Cell.