Jonathan Tilly defied decades of dogma by suggesting that women can make new eggs throughout their lives. Now some of his critics are taking a second look.
Jonathan Tilly likes to gauge the significance of his work by the hair on the backs of his arms. “Look at it standing up,” he says, thrusting out his forearm on a mid-August afternoon. A reproductive biologist at Massachusetts General Hospital in Boston, Tilly was explaining a procedure to retrieve stem cells from the ovaries of a sterile woman. This experiment, he hopes, will help to quell criticism of his most controversial claim: that ovaries have the potential to make eggs indefinitely. This defies the long-held dogma that female mammals are born with all the oocytes (precursors to eggs) they will ever produce, a population that dwindles with age and is exhausted at menopause.
Tilly first challenged that doctrine in 2004, in a paper1 suggesting that the oocytes in mouse ovaries are being replenished by stem cells. If properly understood, such cells could be harnessed to generate fresh eggs for women with fertility problems, or even achieve a goal Tilly has been pursuing for 25 years: delaying or halting menopause. “The hairs are still up,” Tilly says. It “happens every time I think about that experiment”.