The Nobel Prize in Medicine or Physiology will be shared this year by three researchers, two Americans and a Briton, for their studies of embryonic stem cells in mice. Kevin Billinghurst was on the scene for VOA when the announcement was made at the Karolinska Institute in Stockholm.

"The 2007 Nobel Prize in Physiology or medicine goes to Mario Capecchi, Martin Evans and Oliver Smithies for their discoveries of principles for introducing specific gene modifications in mice by the use of embryonic stem cells," said Professor Christer Betsholtz of the Karolinska Institute, announcing the winners of perhaps the most prestigious award in medicine.

Mario Capecchi, orphaned during World War II in his native Italy, made his way to the United States and earned a doctorate from Harvard University in 1967. He is currently Distinguished Professor of Human Genetics and Biology at the University of Utah and a member of the National Academy of Sciences.

Oliver Smithies is a British-born American holding the post of Excellence Professor of Pathology and Laboratory Medicine at the University of North Carolina at Chapel Hill.

Capecchi and Smithies studied the process by which natural selection increases genetic variation in a population by exchange of DNA sequences.

Working together, they set out to prove that this homologous recombination could be used to specifically modify genes in mammalian cells. Their process came to be known as gene targeting.

By 1986, the two began working with Dr. Martin Evans a professor at Cardiff University in Britain and a Fellow of the Royal Academy, who provided the cellular vehicle that Capecchi and Smithies needed by showing that mouse embryonic stem cells would pass on introduced genetic modifications.

Embryos from one mouse strain were injected with stem cells from another strain and carried to term by surrogate mothers. The offspring was subsequently mated, and the presence of stem cell-derived genes was detected in the next generation. These genes would now be inherited according to Mendel's laws.

"Gene targeting has meant a revolution to biomedical sciences because it allows us to study of the function of genes in normal physiology - in healthy conditions, but also in disease," continued Betsholz. "You may object when I say our genes, because mice are mice and men are men. But although we may consider ourselves the multi-tasking crown of evolution, it is actually so that we share approximately 95 percent of our genes with mice. And this means that by studying mouse genetics we can infer the function of our own genes."

Capecchi, Smithies and Evans will share an award of more than $1 million, and they will be invited to Stockholm this December to receive their gold Nobel medallions from Sweden's King Carl XVI Gustaf.