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Médecine de la Reproduction

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Neo-oogenesis in the ovary of vertebrates: An experimental and evolutive point of view Volume 13, issue 1, janvier-mars 2011

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INRA-CNRS-Université de Tours, Physiologie de la reproduction et des comportements, UMR 6175, 37380 Nouzilly, France, INRA, SCRIBE UR1037, Différenciation sexuelle et ovogenèse, Campus de Beaulieu, 35000 Rennes, France, INSERM U-865 et ANIPATH, Faculté de médecine Laennec, 7 rue Guillaume Paradin, 69732 Lyon Cedex 08, France

<p>The arrest of oogenesis around the time of birth in mammalian species was a sort of dogma of reproductive biology, which was recently challenged by the Jonathan Tilly's team who claimed in 2004 and 2005 that a neo-oogenesis takes place in the ovary of adult mouse. Neo-oogenesis would originate from female germline stem cells that are present in either the ovarian surface epithelium or bone marrow. These results present several interpretation errors, and have never been reproduced. Following these publications, novel experiments showed that somatic stem cells in vitro are able to generate “oocyte-like” structures who express some oocyte markers, but are not able to ovulate, to be fertilized and to ensure embryonic development. In contrast, it has been shown recently that stem cells from the mouse ovarian surface epithelium are able to proliferate during several weeks in vitro, to colonize an adult ovary, to give rise to oocytes able to be fertilized and to give offsprings. Hence one can now reproduce a form of neo-oogenesis in vitro, but not in vivo, in adult mammals. From an evolutionary front of view, neo-oogenesis occurs in the ovary of fishes and amphibians, which ensure the ovulation of thousands of oocytes at each sexual season. During evolution of land vertebrates, in particular in mammals, this function would have progressively disappeared.</p><p>Overall, these new data support the possibility to experimentally handle a form of neo-oogenesis in mammals in vitro, and then to restore fertility in women suffering from fecundity disorder.</p>