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Kyoto Univ. team creates ova precursors from iPS cells

KYOTO -- In a world first, Kyoto University researchers have successfully produced oogonia -- cells that can develop into ova -- from induced pluripotent stem (iPS) cells, the team has announced.

    Many details of the mechanism behind the formation of human germ cells remain unclear. The technology developed by the team led by developmental biology professor Michinori Saito could help clarify causes of infertility and lead to the development of reproductive treatments.

    The results will be published on Sept. 21 in the online edition of the U.S. scientific journal "Science."

    The team had previously created cells closely resembling primordial germ cells that can develop into sperm and ova from human iPS cells. However, they had been unable to confirm they were germ cells because the cells did not differentiate any further.

    In the latest experiment, the team created cells resembling primordial germ cells from human iPS cells and combined them with ovarian somatic cells extracted from fetal mice (with the mouse's own germ cells removed), and cultured the mixture for about four months. On the 77th day, the researchers observed gene expression that occurs when a cell develops into an oogonium, and noted that the cells had both become oogonia-shaped and had chromosomes very similar to the germ cell precursors. DNA markers that initialize when a cell becomes an oogonium were furthermore found to be active, and the team concluded they had hit on a technique to differentiate oogonia.

    The researchers will further strive to differentiate oogonia into ova, while also going ahead with similar research using embryonic stem (ES) cells.

    "We'll press forward with our research to produce ova and sperm, and use the results to clarify the process of cell differentiation and DNA reconfiguration," professor Saito said.

    Government guidelines prohibit the creation of fertilized eggs from ova and sperm created from iPS or ES cells.

    (Japanese original by Mai Suganuma, Kyoto Bureau)

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