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Scientists Clone Mice From Hair Follicle Stem Cell
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The stem cells come from adult mice, are relatively easy to obtain and inject, and may represent a good future source of stem cells for animal cloning, the U.S. team said.
"This work opens the door for generating embryonic stem cells (easier than cloning mice) from adult skin stem cells," said Elaine Fuchs, co-senior author of the paper and head of the Laboratory of Mammalian Cell Biology and Development at Rockefeller University in New York City. "If researchers overcome the current technical hurdles of making human embryonic stem cells by nuclear cloning, it may one day be possible to generate tailor-made embryonic stem cells from a patient's skin stem cells," she said.
But the accomplishment so far applies only to mice, another expert added.
"People like to think about human applications, but we need to be careful about that," said Dr. Peter Mombaerts, the paper's other senior author and head of Rockefeller University's Laboratory of Development & Neurogenetics.
The findings are published in the current issue of the Proceedings of the National Academy of Sciences.
Several different varieties of animals have been cloned (Dolly the sheep and Idaho Gem the mule, to name but two) from several different cell types, but the process is notoriously inefficient. Scientists may need 100 oocytes (a precursor to the ovum) to produce just one or two animals.
"Cloning basically doesn't work very well," Mombaerts explained. "It's very inefficient."
Some believe that stem cells, a sort of primal cell which has the capability of differentiating into many other types of cells, would be more efficient because they're undifferentiated -- they're basically "blank slates," waiting to turn into any one of a number of different types of cells.
The process of nuclear transfer, which is how Dolly the sheep was created, involves inserting the nucleus of a donor cell into an unfertilized egg which has had its own nucleus removed.
In this paper, "we show that we can use the nuclei of the adult mouse hair follicle stem cells for nuclear transfer," Fuchs said. "Our studies demonstrate that we can clone mice from hybrid cells composed of the nucleus of an adult skin stem cell and an enucleated (nucleus-removed) unfertilized mouse oocyte."
Overall, the cloning rate using hair follicle stem cells was similar to what has been seen in the past, but the study also yielded an unexpected finding: The rate of cloning efficiency when the stem cells were taken from male mice (5.4 percent) was consistently higher than that of female donors.
"This has been sporadically mentioned here and there, but we now confirm it a bit more systematically," Mombaerts said.
The hair follicle stem cells were more efficient than already-differentiated cells but nowhere near as good as embryonic cells.
"They were better than differentiated cells, but it was not spectacular," Mombaerts said. "It wasn't what we would hope."
But, by trying new cell types, Mombaerts hopes that one day scientists will achieve an "extremely efficient" 20 percent to 30 percent.
SOURCES: Peter Mombaerts, M.D., Ph.D., head, Laboratory of Development & Neurogenetics, Rockefeller University, New York City; Elaine Fuchs, Ph.D., head, Laboratory of Mammalian Cell Biology and Development, Rockefeller University, New York City; Feb. 12-16, 2007, Proceedings of the National Academy of Sciences
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