From Nature:
Researchers in China today announced a discovery that challenges a canonical belief in reproductive biology: that women are born with a set number of immature egg cells, called oocytes, which become depleted with age. In a paper in Nature Cell Biology,1 the Chinese team reports that it has found precursors to oocytes in adult mice. When the researchers transplanted those cells into sterilized mice, they produced offspring — a finding that feeds into an ongoing debate about the limits of mammalian fertility.
“It provides a smoking gun,” says Jonathan Tilly of Massachusetts General Hospital in Boston, who was not involved in the work but has previously published evidence that new eggs can be formed in adult mice in a series of argument-sparking papers.2 Although the current work hasn't settled the question, Tilly says, it represents an addition to the “critical mass of data” suggesting that old ovaries can produce new eggs, a finding that some say could have implications for fertility medicine.
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