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    Women Not Born With Lifetime Supply of Eggs?

    Animal Study Shows Mammals Have a Reserve of Egg-Producing Follicles

    Finding Challenges Basic Reproductive Biology Beliefs continued...

    Researchers found that the number of healthy follicles actually decreased relatively slowly despite this rapid loss of follicles. That finding shows that healthy egg-producing follicles must be produced somewhere in young mouse ovaries.

    To test this theory, researchers treated the young mice with a chemical that kills egg cells and instead found that the mice still produced viable eggs in adulthood.

    Researchers say the results show that a reserve of stem cells that form the building blocks for reproductive cells must exist in female mice as they do in male mammals. But more research is needed to determine how they function and what causes them to decline after adolescence.

    Implications for Female Fertility

    In an editorial that accompanies the study, Allan C. Spradling of the Carnegie Medical Institute Laboratory in Baltimore, Md., says the study raises many interesting and important questions.

    For example, the location and the number of these 'reserve' or germ stem cells in females will need to be determined.

    In addition, "the question on everyone's lips will be whether there are germline stem cells in the human ovary."

    Spradling says these cells might have easily been missed in humans for the same reasons they were missed in mice for so long -- they were thought to be rare.

    He says the work also raises "the strong possibility" that the rapid decline in female fertility that occurs after age 30 is caused by the depletion of these 'reserved' cells coupled with an age-related decline in healthy egg-producing follicles.

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