Silicon Investor (SI) -- The First Internet Community

STOCKTALK

We've detected that you're using an ad content blocking browser plug-in or feature. Ads provide a critical source of revenue to the continued operation of Silicon Investor. We ask that you disable ad blocking while on Silicon Investor in the best interests of our community. If you are not using an ad blocker but are still receiving this message, make sure your browser's tracking protection is set to the 'standard' level.

Biotech / Medical : Biotransplant(BTRN) -- Ignore unavailable to you. Want to Upgrade?

To: Arthur Radley who wrote (1321)	5/14/2002 8:42:01 PM
From: Arthur Radley	Read Replies (1) \| Respond to of 1475

Study Shows Genetic Basis for Cloning Failure Tue May 14, 5:45 PM ET By Alison McCook NEW YORK (Reuters Health) - Only a small fraction of cloned mouse embryos properly express a gene that is crucial for normal development, University of Pennsylvania researchers report. This finding may explain why so few attempts to clone embryos are successful, they note. "Basically, it's a miracle that cloning actually works," study author Dr. K. John McLaughlin told Reuters Health. In the procedure commonly referred to as therapeutic cloning, scientists would extract the nucleus of a patient's cell and transplant it into an egg that has been stripped of its own nucleus. The egg would then be coaxed to grow into an embryo, which would contain stem cells. One day, scientists hope, they will be able to use stem cells formed in this way to replace tissue damaged by stroke, Parkinson's disease (news - web sites), diabetes, heart attack and many other conditions. "Reproductive" cloning, in contrast, results in living, cloned animals such as Dolly the sheep. In the study, the researchers tested cloned mouse embryos for the presence of the gene Oct4, which is expressed in embryos. Finding Oct4 in the embryo would indicate that the nucleus from the donor cell, which did not originally contain Oct4, had been successfully coaxed into becoming an embryo. Examining the presence and levels of Oct4 in the embryo, the investigators found that only 34% of the embryos expressed Oct4 in the right places during the crucial first days of development. Furthermore, many of those that contained Oct4 were expressing it at abnormal levels, according to the report published in the May 15th issue of Genes and Development. In a further test of the viability of these embryos, McLaughlin and colleagues placed them in environments that mimicked the uterus. They found that less than half of cloned embryos that continued to grow expressed Oct4, and at much lower levels than embryos formed by in vitro fertilization. The small number of cloned embryos that did develop to the stage where they could produce stem cells--after 6 to 7 days of development--expressed the right amount of Oct4. McLaughlin said that this finding suggests that researchers conducting both reproductive and therapeutic cloning could "weed out the weeds" among clones by testing each in the early days of development for the presence of Oct4. If the gene is not expressed properly, McLaughlin said, investigators could be confident in abandoning their efforts to develop stem cells from that embryo. "If you don't have Oct4 in the right place at the right time, at the right levels, you won't get an embryo," he said. McLaughlin added that he suspects other genes are likely not properly expressed in doomed cloned embryos, and that Oct4 expression may, in fact, be controlled by another gene that more directly relates to whether or not a cloned embryo will develop successfully. The study also illustrates, he noted, just how difficult it is to generate a cloned embryo