Contrary to long-held scientific views that the number of oocytes (eggs) in the ovaries of most mammals is fixed at birth, scientists report that new oocyte-containing follicles continue to develop in the ovaries of adult mice. The research suggests that these new oocytes come from stem cells located in the ovary. The study, supported by the National Institute on Aging (NIA), one of the National Institutes of Health, was conducted by Jonathan L. Tilly, Ph.D., and colleagues at Massachusetts General Hospital and Harvard Medical School and appears in the March 11, 2004, issue of Nature* .
"If this finding is confirmed by others, Dr. Tilly and his colleagues would seem to have rewritten the book on reproductive biology--at least for mice," says Frank Bellino, Ph.D., Deputy Associate Director of the Biology of Aging Program at the NIA. "Further study about how oocyte production in adults is controlled might eventually make it possible to regulate the rate at which oocytes are formed in women. This, in turn, could possibly be used to delay premature ovarian failure as well as menopause and may help women maintain their health for a longer period of time."
Tillys group began by comparing the numbers of healthy and degenerating follicles in the ovaries of a particular strain of mice from birth through young adulthood. They reasoned that if the number of follicles in the ovary is set at or shortly after birth, then the loss of healthy follicles over time would be accounted for by the total number of follicles undergoing atresia (degeneration) during the same time period. Instead, they found that the incidence of atretic follicles was significantly greater than the loss over time of healthy or non-atretic follicles. Evidence that degenerating follicles disappeared from the ovaries within 3 days (and, thus, were not being counted more than once) suggested to the investigators that the ovaries continue to produce new oocyte-containing follicles into adulthood.
Karin Kolsky | EurekAlert!
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