Cloned Human Embryos Successfully Reprogrammed Using Human – But Not Animal – Eggs
New study questions ability of human-animal hybrids to generate stem cells
Since the cloning of Dolly the Sheep over a decade ago, somatic cell nuclear transfer (SCNT) has been considered a promising way to generate personalized stem cells to repair the body without fear of tissue rejection. Due to the serious shortage of human donor eggs, cows, rabbits, and other animals have long been considered an attractive surrogate source of eggs. Although previous reports have documented the formation of cloned embryos using both human and animal eggs, to-date, there has been no data indicating whether -and to what extent the donor DNA was reprogrammed.
This new study looked at the reprogramming of human cells using eggs obtained from human and animal sources, and shows for the first time that the donor DNA in the cloned human embryos is extensively reprogrammed through extensive up-regulation (‘turning on’ of genes) with similar expression patterns to normal human embryos. Nearly all of the key differentially-expressed genes were activated in the human clones. In distinct contrast, the majority of these genes were down-regulated or silenced in the human-animal hybrids.
“We examined the factors recently used to reprogram skin cells (to induce pluripotent stem cells),” said
Previous studies have confirmed the ability of animal eggs to support interspecies cell division to the embryo stage, and in a few closely-related bovid species, successful development to term. However, there are clear differences in compatibility. Distantly-related animal combinations generally arrest at the cleavage-stage, although there have been reports of blastocyst formation. Our group and others have successfully used eggs to clone closely-related species (for instance, we cloned two endangered species – the guar and banteng using cow eggs). Rabbit eggs have also been used to generate embryos using cells from cats and panda, among others. However, it remains unknown whether the DNA in the later combinations was fully reprogrammed. Importantly, except for a study carried out in
Wide scale application of stem cell technology will require a solution to the problem of rejection. This report suggests that adult cells can be successfully reprogrammed using human eggs, and that scientists may soon have two ways (SCNT and induced pluripotent stem cell technology) to reprogram adult cells into stem cells. However, until this is achieved, clinical trials are likely to be limited to immune-privileged sites in the body, such as the use of cells in the central nervous system, or the transplantation of ACT’s retinal cells into the eye to prevent blindness.
“Producing millions of patient-specific stem cell lines is commercially unviable,” stated
The paper’s other authors are
Link to article: www.liebertpub.com/clo
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