Researchers announced today in London that they have succeeded in cultivating a newly discovered type of mammalian embryonic stem (ES) cell. Dubbed EpiSC, the cells are isolated from post-implantation mouse and rat embryos. They are more like human ES cells than are existing mouse ES cells and thus may offer a new and controversy-free model for understanding how human cells grow and differentiate, the researchers say.
The work, published online by Nature today, was done independently by two groups. One group, led by Ronald McKay of the U.S. National Institute of Neurological Disorders and Stroke with colleagues at Oxford University in the U.K., focused on mice. The other group, headed by Roger Pedersen and Ludovic Vallier, both of Cambridge University, U.K., experimented with rats as well.
"This is a new type of pluripotent cell," meaning that it can grow into any kind of body tissue, says McKay. Traditional mouse ES cells, he explains, cannot tell us a great deal about human ones because mouse cells are "more primitive." For example, mouse cells need the growth factor LIF (leukemia inhibitory factor) whereas human ES cells, like other stem cells, grow better with this pathway inhibited. But now, his group has found a mouse stem cell that behaves like human stem cells do.
The EpiSCs come from the epiblast, the innermost cells of a mouse embryo, 5.5 days after implantation in the uterus. Like human ES cells, they don't thrive with LIF present, and they share patterns of gene expression and cell surface markers with human cells. The cells represent a more advanced stage of development, a "missing link," between traditional mouse ES cells and cells that are beginning to differentiate, McKay says. "Most people thought you couldn't make [pluripotent] cell lines after implantation," he adds.
Pedersen says the rat EpiSCs resemble those of the mouse, and he predicts that scientists will be able to generate such cells "from most or all mammals." Cell lines developed from these stem cells will be useful as models for accelerating the development of human embryonic stem cells into tissues that can be used to treat patients, he says.
Stem cell researcher Renee Reijo Pera of Stanford University in Palo Alto, California, is optimistic that new cells will be useful in elucidating the workings of human ES cells. The work, she adds, suggests scientists may be able to derive new types of ES cell lines--including from humans--that "may ultimately be more suitable for specialized purposes."
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