'Missing link' to revolutionise use of stem cells

Two teams of scientists have discovered independently a new type of stem cell they believe could lead to better treatments for incurable diseases.

Researchers from Oxford and Cambridge universities made the discovery in laboratory mice and rats. They found that the new cells behave just like a human stem cell - raising the prospect of better animal models of human illnesses.

The study, published in the journal Nature, is described as the "missing link" between animal and human stem cells that could eventually revolutionise the development of treatments for patients.

Stem cells are the unspecialised "mother" cells of the body that have the power to develop into any of the scores of specialised tissues - from the muscle cells of the heart to the nerve cells of the brain.

Scientists hope to find a way of harvesting human stem cells, either from embryos or from adult tissue, in order to grow replacement body parts in the laboratory for treating defective tissue rather than relying on organ transplants.

The best stem cells in terms of their ability to become specialists are derived from early embryos but scientists have been puzzled as to why embryonic stem cells from mice appear to behave differently to those from humans.

They thought these differences could be explained because the cells come from different species but the latest study suggests that it is probably due to the timing of stem cell harvesting. The new stem cell, derived initially from mice, was taken at a later embryonic stage than usual. This mouse stem was remarkable for how different it was to normal mouse stem cells and how similar it was to human stem cells.

"These findings suggest that human embryonic stem cells originate at a later stage of development than previously thought," said Sir Richard Gardner, who led the Oxford team.

"The ultimate ideal would be to help a patient who requires regeneration of parts of the body by taking stem cells in a biopsy and re-differentiating the cells to grow them into the needed part of the body."

Stem cells from the mice embryos were normally taken at the stage of the blastocyst, which develops between three and four days after conception. The new stem cell was taken from a structure in the embryo called the epiblast, which develops when the embryo is a week old and capable of implanting itself into the womb.

"The epiblast stem cells, as they have been named, constitute the 'missing link' between mouse and human embryonic stem cells," said Professor Roger Pedersen, who led the Cambridge research team.

"On a molecular level, epiblast stem cells are more similar to human embryonic stem cells than to mouse embryonic stem cells," he said.

"The differences between mouse and human embryonic stem cells that we had attributed to species differences may actually come down to the developmental stages from which the cells emerge.

"Our hope is that pinpointing the developmental stage when human embryonic stem cells originate will help scientists who are using cells to develop cures for injuries and disease."