Ralph, the fertile cloned rat unveiled

A team of French scientists have become the first to successfully clone rats from adult cells, further increasing the number of mammals that have been cloned in this way. One of the clones, named Ralph, has gone on to father a litter of healthy pups, now two months old. The reason for cloning rats was to produce genetically identical animals for use in medical research, but in order to do so the scientists had to overcome a problem with rat physiology. Rat eggs start to activate almost immediately after leaving the ovaries, so there is only a small window of time in which the genetic material of the animal being cloned can be introduced.

The team, led by researchers at the National Institute of Agricultural Research at Jouy en Josas, France, cloned both male and female rats using SCNT (somatic cell nuclear transfer ), the technique used to create Dolly the sheep. In order to overcome the problem with the eggs, they used a chemical called MG132 (which stops cells dividing) to delay activation and to stabilise them, before transferring in the new DNA. The scientists managed to create 129 cloned embryos, which were implanted into two adult female rats. One became pregnant with three male rats, one of which died shortly after birth. When the technique was repeated, two female cloned rats were born. Despite a high failure rate, the rats that were successfully cloned were able to be mated and produced normal, healthy pups. The research will be published in the journal Science.

Rats are one of the most commonly used animal models in human disease research. Cloning will provide a valuable source of genetically identical rats for research and could also enable genetic manipulation of the rodents that would allow scientists to study specific disorders that affect humans. Robert Lanza, the medical director of Advanced Cell Technology (ACT), a US-based biotechnology company that has also been trying to clone rats, welcomed the achievement of the French team. 'Nobody up to now has had any success in cloning the rat', he said, adding 'this is extremely important. We now have the potential to create all sorts of animal models to study diseases'.