NewScientist.com news service
New Scientist and AFP

The discovery of a mouse embryonic stem cell that is a near-perfect match to human cells will speed research in regenerative medicine and treatments for conditions such as Parkinson's and diabetes, researchers say.

Embryonic stem cells from mice are usually taken from very early stage embryos, called blastocysts (see Instant Expert: Stem Cells). These cells are significantly different from human cells and so have limited value.

Roger Pedersen at Cambridge University, UK, and colleagues took cells from the mouse embryo at a later stage in its development, when it is an epiblast. They found that epiblast stem cells, taken from the innermost layer of week-old rodent embryos, shared many of the same properties of human embryonic stem cells.

"They are a missing link between mouse and human embryonic stem cells," says Pedersen, who led the study. The new cells will provide a better model in testing potential therapies for human diseases and injuries, he adds.

New therapies

Another group, led by Richard Gardner at Oxford University, UK, has announced similar findings.

Both studies were hailed by other scientists as a breakthrough that would shed light on the origin of human embryo stem cells and help fulfil the rich promise of cell-based medicine.

Adult bone-marrow stem cells are already used in the treatment of leukaemia, and experiments suggest stems cells could also yield effective treatments for numerous other illnesses, including Alzheimer's and spinal-cord injury.

Scientists have successfully grown mice embryo stem-cell lines in the laboratory for decades, and human ones since the late 1990s.

But until now, human and mice stem cells looked and behaved very differently, limiting the parallels that could be drawn between the two species, and raising questions about what accounted for the divergence.

Late breakthrough

"It was perplexing," Pedersen says. "Was is it the evolutionary divergence of mice and men, or was there a developmental explanation, reflecting different stages of growth?"

This question spurred Pedersen and his team to challenge conventional wisdom and see whether the bio-chemical conditions used to maintain human embryo stem cells might work for mice too.

Previous attempts had failed. But when the researchers applied the human-specific molecular cocktail to a later stage of the mouse embryo, rather than the three-day old blastocyst stage from which stem cells had always been drawn, suddenly it worked.

"Comparative analyses suggest that the new cells may have more in common with human embryo stem cells" than the ones taken earlier in the life cycle from mice, says stem cell biologist Ian Chambers, the University of Edinburgh.

Exciting findings

"These are exciting findings that hint at ways in which it may be possible to alter the culture conditions for human embryo stem cells in order to make their maintenance more straightforward and malleable," says Chambers, who was not involved in the studies.

Kevin Eggan, at the Harvard Stem Cell Institute, US, also welcomed the studies, saying they could "shed light on the origin and nature of human embryonic stem cells".

The discovery of the epiblast stem cells in mice should make it easier to isolate stem cells in other species, including livestock, as well as mice genetically modified to express a disease so that it can be studied, Pederson says.

Journal references: Nature (DOI:10.1038/nature05972 and DOI:10.1038/nature05950).