Do women produce new eggs as they age?

• Oocyte-producing cells found in mouse, human adult ovaries

• Number of mitotic cell divisions suggests eggs produced after prenatal period

Rethinking the “biological clock,” a new study suggests that women’s ovaries continue to form new eggs throughout life. Analyzing an earlier study, reproductive biologists argue in PLoS Genetics that oocyte-producing stem cells (OSCs) in ovaries continue to divide after birth, producing new eggs even into adulthood.

In the traditional view, female mammals’ ovaries at birth contain all the eggs they will have throughout life. Recent research, however, has shown that adult mouse and human ovaries contain OSCs capable of dividing and creating new oocytes. In a study published in February in PLoS Genetics, researchers used a new technique to count a cell’s “depth,” or how many times it has divided, finding that ovaries of older mice released eggs with significantly greater depth than those of younger mice.

While the traditional view holds that eggs are released throughout life in the order of their production during the prenatal period, the difference in the number of mitotic cell divisions was far too great to support that conclusion. The more likely cause, the biologists argue, is that the progenitor OSCs continue to divide as the animal ages, creating eggs with greater depth later in life. Further research in humans is needed, but oocyte production in women may be far more likely than previously believed.

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