June 28 (HealthDay News) -- Scientists have discovered a new type of rodent embryonic stem cell that is more akin to its human counterparts than current mouse stem cells.

The new mouse embryonic stem cells could provide a useful model to further understanding of human stem cells.

"The real advantage is that you now have another model to look at the underlying mechanisms related to stem cells becoming differentiated," said Paul Sanberg, distinguished professor of neurosurgery and director of the University of South Florida Center for Aging and Brain Repair in Tampa. "It's not a clinically oriented study, but it can be used for core research."

The findings, by two different groups of researchers, are published online June 27 in the journal Nature.

Embryonic stem cells are pluripotent, which means they have the ability to develop into virtually any cell type in the body. The hope is that these cells may one day lead to treatments or cures for diseases such as diabetes, liver failure, spinal injury, stroke, Alzheimer's disease and heart disease.

However, harvesting stem cells involves destroying a viable human embryo, a practice many Americans object to on moral grounds. Embryonic stem cell research in the United States has been severely limited since August 2001, when President George Bush placed limits on federal funding of the field. Now, federal funds can only be used to study stem cell lines derived from embryos that had been destroyed before the 2001 date.

A bill recently passed by the Democratic-led Congress sought to lift that restriction, but Bush vetoed the proposed legislation.

Despite their purported potential, human embryonic stem cells remain largely a mystery to scientists, who are still struggling to understand how they manage to differentiate into so many different cell types.

Mouse embryonic stem cells are also pluripotent. But, said Ronald McKay, senior author of the first paper and a stem cell scientist with the U.S. National Institutes of Health, "there's very good evidence that the two [mouse stem] cells are different. There are different systems that regulate growth. We went back to the mouse to see if we could find another pluripotent cell."

And they and another research group in the United Kingdom succeeded, as documented in Nature.

"That's what we found," McKay continued. "We found a new kind of pluripotent cell in the mouse which behaves like a human cell."

The newly discovered cells were isolated from rodent embryos after they had implanted into the uterine wall. Previously, scientists had thought that embryonic stem cells could only be obtained before implantation into the uterus. The new cells come from a tissue called the epiblast.

The new mouse cells, called EpiSCs (post-implantation epiblast-derived stem cells), grow like human cells, have similar patterns of gene expression and cell surface markers and, of course, are pluripotent.

The two groups of researchers basically came up with the same results.

"It's nice to see two groups substantiate something. You've got replication here," Sanberg said. "Basically, they're showing that they can create a mouse stem cell that is very similar to a human stem cell."

The implications are twofold.

"One is a research implication," McKay said. "If you're interested in pluripotency, then to find a new type of pluripotent cell is very interesting, because you can compare the two mouse types. If you're operating in the same species, you can compare very precisely two types of cells that are poised to differentiate into all the cells of the body.

"The second thing that's interesting is they're going to teach us how to control differentiation of embryonic stem cells," he added. "That's both scientifically interesting, and it's the reason that everybody is excited in a more general sense."

Dr. Darwin Prockop is a professor of biochemistry and director of the Center for Gene Therapy at Tulane University Health Sciences Center.

He called the research "solid, important work. It's opening the window to how the human body develops from the earliest embryos on up. It gives us background on the genes involved, how the expression goes and the time course of events."

SOURCES: Paul Sanberg, Ph.D., D.Sc., distinguished professor, neurosurgery, and director, University of South Florida Center for Aging and Brain Repair, Tampa; Ronald D.G. McKay, Ph.D., stem cell scientist, U.S. National Institutes of Health, Bethesda, Md.; Darwin Prockop, M.D., Ph.D., professor, biochemistry, and director, Center for Gene Therapy, Tulane University Health Sciences Center, New Orleans; June 27, 2007, Nature online