Dr. Hans Schoeler and his team at the University of Pennsylvania’s School of Veterinary Medicine have concluded that a gene, Oct4, plays a pivotal role in genetic reprogramming and may explain the high failure rate in organism cloning (Genes and Development, May 15, 2002). The Oct4 gene encodes a transcription factor that is specifically expressed in the germ-line, pluripotent cells of the pre-gastrulation embryo and stem cells derived from the early embryo.
During cloning, the genetic material taken from a cell of an adult animal was placed inside an enucleated unfertilized egg. The DNA must abandon its previous mission in the presumably already specialized donor cell and assume the new responsibilities to direct the egg to grow, divide, and become a new individual animal. A lot of things can go wrong and they normally do. About 1% of the eggs with transferred nucleus would go on to become an animal.
Dr. Schoeler’s team found that about 10% of the early embryos they studied showed proper activity of Oct4 and that erroneous activity of Oct4 was correlated with abnormalities of the embryo’s development. Oct4 is important but is not the only gene that plays a key role in the DNA’s reprogramming. Other genes could contribute to the failure of development as well.
Dr. Irving L. Weissman of Stanford University, one of the prominent investigators in stem cell research, recently penned a “Sounding Board” column article titled “Stem cells — scientific, medical, and political issues” in the May 16, 2002 issue of the New England Journal of Medicine. “In true transdifferentiation, the differentiated cells in the second tissue or organ must arise solely from single cells of the first tissue, and the differentiated cells must have not only the appearance but also the function of the second tissue,” said Dr. Weissman in the article.
(Discovery Medicine, Vol. 1, No. 8, p12, 2002)