(Reuters) - Scientists from Britain and Japan shared a Nobel Prize on Monday for the discovery that adult cells can be transformed back into embryo-like stem cells that may one day regrow tissue in damaged brains, hearts or other organs.

John Gurdon, 79, of the Gurdon Institute in Cambridge, Britain and Shinya Yamanaka, 50, of Kyoto University in Japan, discovered ways to create tissue that would act like embryonic cells, without the need to harvest embryos.

They share the $1.2 million Nobel Prize for Medicine, for work Gurdon began 50 years ago and Yamanaka capped with a 2006 experiment that transformed the field of "regenerative medicine" - the field of curing disease by regrowing healthy tissue.

"These groundbreaking discoveries have completely changed our view of the development and specialization of cells," the Nobel Assembly at Stockholm's Karolinska Institute said.

All of the body's tissue starts as stem cells, before developing into skin, blood, nerves, muscle and bone. The big hope for stem cells is that they can be used to replace damaged tissue in everything from spinal cord injuries to Parkinson's disease.

Scientists once thought it was impossible to turn adult tissue back into stem cells, which meant that new stem cells could only be created by harvesting embryos - a practice that raised ethical qualms in some countries and also means that implanted cells might be rejected by the body.

In 1958, Gurdon was the first scientist to clone an animal, producing a healthy tadpole from the egg of a frog with DNA from another tadpole's intestinal cell. That showed developed cells still carry the information needed to make every cell in the body, decades before other scientists made headlines around the world by cloning the first mammal, Dolly the sheep.

More than 40 years later, Yamanaka produced mouse stem cells from adult mouse skin cells, by inserting a few genes. His breakthrough effectively showed that the development that takes place in adult tissue could be reversed, turning adult cells back into cells that behave like embryos. The new stem cells are known as "induced pluripotency stem cells", or iPS cells.

"The eventual aim is to provide replacement cells of all kinds," Gurdon's Institute explains on its website.

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