Hum. Reprod. Advance Access originally published online on July 1, 2008
Human Reproduction 2008 23(10):2326-2330; doi:10.1093/humrep/den249
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The oocyte population is not renewed in transplanted or irradiated adult ovaries
1 Department of Genetics and Development, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA 2 Center for Reproductive Medicine and Infertility, Weill Medical College of Cornell University, New York, NY 10021, USA
3 Correspondence address. E-mail: vep1{at}columbia.edu
BACKGROUND: According to conventional theory, the oocyte population is not renewed in mammalian ovaries after birth. A new hypothesis proposes that oocytes are generated continuously from haematopoietic progenitor cells. There is, however, no evidence that they can ovulate, although they may partially restore fertility by organizing ‘helper follicles’. The hypothesis that follicles can form de novo in adult ovaries has been tested in a transplant model.
METHODS: Ovaries from adult mice were transplanted under the kidney capsule or into the ovarian bursa of histocompatible, transgenic CAG::H2B-EGFP host animals. Some donors were sterilized before transplantation by X-irradiation to ensure ‘empty niches’ were available for repopulation. The phenotype of follicular oocytes at 2, 4 and 8 weeks post-transplantation was scored by epifluorescence.
RESULTS: A total of 819 oocytes were examined in 30 ovarian grafts. None expressed green fluorescence, as would be predicted if they had formed de novo from germ cell progenitors in the systemic circulation of the host. Furthermore, small follicles eliminated by irradiation were not replaced in transplanted ovaries, and the few growing follicles present were apparently survivors of the original population.
CONCLUSIONS: No evidence was found to support the hypothesis that progenitor cells from extra-ovarian sources can repopulate the adult ovary. The findings are consistent with the conventional view that a limited number of oocytes are formed before birth and declines with age. The study did not, however, rule out the possibility that germline stem cells may reside in the adult ovary.
Key words: follicle/ovary/regeneration/transplantation/X-irradiation
Submitted on April 28, 2008; resubmitted on May 23, 2008; accepted on June 4, 2008.
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