Also known as somatic cell nuclear transfer, therapeutic cloning is a promising approach to create individually customized cellular therapies for treating certain disorders. Demonstrated in mice but not in humans, it begins with stem cells derived from a cloned embryo. But if cloned embryos can't produce normal organisms, how can they produce normal stem cells?
Analyzing the complete gene-expression profiles of both cloned and fertilization-derived stem cells in mice, scientists at Whitehead Institute for Biomedical Research now have concluded that the two are, in fact, indistinguishable.
"This paper demonstrates clearly that it doesn't matter if a stem cell has been derived from a cloned embryo or from a fertilized embryo," says Whitehead Member Rudolf Jaenisch, senior author on the paper that will appear in the online the week of January 16 in the Proceedings of the National Academy of Sciences. "Both can be equally good for therapy."
To create a clone, a scientist removes the nucleus from a donor cell, then places it into an egg from which the nucleus has been removed. The researcher then tricks the egg into thinking it's been fertilized. The egg develops into a blastocyst, an early stage embryo consisting of no more than 100 or so cells. The scientist can then either remove the stem cells from this blastocyst, or place it into a uterus where it has the potential to develop into a fetus.
Here's where things get complicated. The original donated nucleus may have come from, say, a skin cell. For a viable fetus to develop, the egg needs to reprogram the genome of the skin cell, shutting off genes specific for skin tissue and turning on genes needed for embryonic development, genes that are normally dormant in tissue-specific cells
Source:Whitehead Institute for Biomedical Research