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One-Parent Embryos: A Step Ahead in Stem Cells PHILADELPHIA _ When the subject is stem cell research, the term embryo is not only ethically charged, but increasingly hard to define. Now, University of Pennsylvania researchers have stretched the definition even further. In studies with mice, they created embryos using genetic material from only one parent _ either a mother or a father. This dead-ended the embryos' development, but not before the organisms reached the stage where they contained embryonic stem cells _ the precious precursors of all types of specialized cells. In a first-of-its-kind experiment, these embryonic stem cells were used to reconstitute the blood systems of adult mice whose own blood cells were destroyed by radiation. The study, published last month in the journal Genes & Development, is another step forward for the emerging field of regenerative medicine, which aims to find ways to repair and rebuild human tissue. If the same approach works in humans _ a big if _ then patients could be given stem cell treatments that their immune systems would not reject. "In humans, this could provide a therapeutic route for both genders," said senior author K. John McLaughlin, a researcher at the University of Pennsylvania's New Bolton Center. "Members of either sex can use this technique to produce compatible stem cells, much like you might donate blood for your own use." For most people, the concept of a human "embryo" is straightforward: After a man's sperm fertilizes a woman's egg, it grows into a ball of cells that implants and develops in a woman's uterus. But as animal cloning has shown, embryos can be created by replacing the nuclear DNA of an egg with the DNA of a body cell _ say, a skin cell. No sperm needed. With the proper chemical and electrical cues, an embryo also can develop from nothing more than an egg. This is true even in humans because the unfertilized egg contains the full human genome. (Fertilization signals the egg to get rid of half of its genetic material to make room for the sperm's contribution.) A few creatures, such as the Komodo dragon, can go all the way to giving birth with this one-parent reproductive process, called "parthenogenesis." In contrast, human parthenogenetic embryos soon die because parts of their genetic code are unreadable. To be correctly read, these genes need chemical tags inherited from the father as well as the mother _ tags that medical science cannot artificially replace. Even though human embryos made with mother-only genes are short-lived, they could be a source of stem cells. In January, an Italian study published in Fertility & Sterility showed that parthenogenetic human embryos could grow for five days, the point at which embryonic stem cells briefly exist. McLaughlin and his colleagues wanted to find out, at least in mice, whether stem cells derived from one-parent-only embryos would retain their therapeutic power, or be as compromised as the embryos. It turned out that the embryonic stem cells were still powerful. In a lab dish, they were chemically signaled to turn into blood stem cells. These blood stem cells went on to reconstitute blood when transplanted to the irradiated mice. The scientists also carried out the male version of parthenogenesis, called androgenesis. They removed the nuclear DNA from an egg and slipped in two sperm nuclei from a mouse. Two sperm nuclei were needed because, just as in humans, each sperm carries half the necessary genetic material. These androgenetic embryonic stem cells, like the parthenogenetic version, could be signaled in a lab dish to spawn blood stem cells that, when transplanted into irradiated mice, reconstituted the destroyed blood systems of the mice. Even if this method for deriving therapeutic stem cells works in humans, it is not likely to quell the objections of those who equate destroying human embryos with murder. Previously, researchers at other labs used mice to create embryolike entities that yielded stem cells but were incapable of implanting in a uterus; the scientists were criticized for intentionally making "disabled" embryos. Still, McLaughlin believes that using "uniparental" embryos to produce stem cell therapies has advantages over using cloned embryos for that purpose. "It's ethically more attractive, and very efficient compared to therapeutic cloning," he said. ___ (c) 2007, The Philadelphia Inquirer. Visit Philadelphia Online, the Inquirer's World Wide Web site, at http://www.philly.com/ Distributed by McClatchy-Tribune Information Services. For reprints, email [log in to unmask], call 800-374-7985 or 847-635-6550, send a fax to 847-635-6968, or write to The Permissions Group Inc., 1247 Milwaukee Ave., Suite 303, Glenview, IL 60025, USA. Source: The Philadelphia Inquirer ---------------------------------------------------------------------- To sign-off Parkinsn send a message to: mailto:[log in to unmask] In the body of the message put: signoff parkinsn