WOBURN, Mass., Aug. 27 U.S. researchers using CRi's Oosight(TM) imaging system have developed a gene transfer technique that has potential to prevent inherited diseases passed on from mothers to their children through mutated DNA in cell mitochondria. The research, which demonstrated the technique in rhesus monkeys, appears in the Aug. 26 issue of the journal Nature.
The group, headed by Dr. Shoukhrat Mitalipov of the Oregon National Primate Research Center and the Oregon Stem Cell Center, extracted the nuclear DNA from the mother's egg, guided by the Oosight system, and transplanted it into another egg that had the nucleus removed. The technique allowed the mother to pass along her nuclear genetic material to her offspring without her mitochondrial DNA. The eggs were fertilized and transplanted into surrogate mothers, resulting in the birth of four apparently healthy monkeys. Defects in DNA of mitochondria, the cell's "power plants," are associated with a wide range of human diseases.
The Oosight system solved a key problem in avoiding damage to the nuclear DNA during the transfer procedure by providing a non-invasive imaging technique for visualizing the genetic material. Traditional visualization methods employ a stain or involve exposure to ultraviolet light, either of which can damage DNA. The Oregon team had used the Oosight system in previous research, published in Nature in 2007, that provided a foundation for the current study. In that research, they cloned rhesus monkey embryos and used them to create embryonic stem cells.
The Oosight system uses polarized light to generate high-contrast, real-time images of biological features such as the spindle apparatus housing the chromosomes and other filamentous structures within the egg, such as the multi-layer zona pellucida, without the addition of toxic stains or labels, while simultaneously generating useful quantitative data of their structural composition. Two of the four offspring, Spindler and Spindy, were named after the spindle, which is what the Oosight system is used to visualize.
"This study underscores the potential of the Oosight system to advance reproductive medicine and highlights the enabling capabilities or our polarized light technology," said George Abe, president and CEO of CRi.
"With this advance, the Oosight imaging system, which is already widely used in fertility clinics, has offered new insights and possibilities into reproductive health and medicine," said Gary Borisy, director and CEO of the Marine Biological Laboratory (MBL) in Woods Hole, MA. The Oosight system is based on imaging technology originally developed by MBL scientists Rudolf Oldenbourg and Michael Shribek, working in collaboration with David Keefe, M.D., of the University of South Florida College of Medicine.
In in vitro fertilization (IVF) the Oosight system is used as an aid to intracytosplasmic sperm injection (ICSI). The system not only provides assurance that the genetic material is not damaged by the injection needle, but it can also be used as a measurement tool to assess egg viability in both fresh and frozen eggs. Data show that an egg with a weak or malformed spindle and inner layer zona as measured with the system is much less likely to result in pregnancy.
Other scientists have welcomed news of the advance. Mitochondria-expert Douglas Wallace of the University of California, Irvine, said "results were exciting" and the technique is "potentially very interesting." Although he did caution that "there are safety issues that are going to need to be addressed before one could think about it in humans."
The Nature article reported that 15 embryos were transplanted into nine surrogate mothers; three became pregnant, one with twins, and four offspring were born (only three of these offspring have been reported in the Nature paper) The success rate is similar to that of conventional in vitro fertilization.
A sample movie of the enucleation process that Dr. Mitalipov used is available at http://www.cri-inc.com/multimedia/Oosight_SCNT_Enucleation_Rhesus_Monkey.avi, (movie courtesy Dr. Mitalipov, OHSU).
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