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Scientists Reveal Key Barrier to Reprogramming Human Zygotes



So far, however, nuclear transfer has not yet been successful in human cells. Many scientists have turned instead to stem cell lines created by reprogramming adult cells (usually skin cells) taken from patients. Because of the challenges in obtaining eggs, Eggan's team, in collaboration with Melton's lab, decided to pursue an alternative: rather than transferring a patient's DNA into an unfertilized egg, they would see if they could achieve the same result by transferring the DNA into an embryo.

The researchers isolated the embryos that were still single cells—fertilized eggs that had not yet developed any further. When they transferred nuclear DNA into the embryos, development continued through the early stages, but then halted about four days later. This was in contrast to what they observed when they used the identical technique to transfer DNA to single-cell mouse embryos, which developed into more mature embryos expressing the transferred genes.

The team then traced the developmental arrest to a specific cellular failure: the embryos never turned on the genes contained in the transferred nucleus. It's not clear what prevents this essential activity from occurring in the human cells, but Eggan says his team's finding could focus the attention of other researchers as they work to make somatic cell nuclear transfer a viable method for producing disease-specific stem cell lines.

Their report was first published online October 4 in Nature Communications.

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