QUEBEC CITY, CANADA--Cells in the bone marrow and blood are a source of egg cells in the ovary, a reproductive biologist announced here today at the annual meeting of the Society for the Study of Reproduction. But the remarkable claim, which has kept this gathering of 1500 biologists buzzing, was met with skepticism. If true, the idea would have major implications for blood and bone marrow donation, and for patients undergoing cancer treatments that destroy fertility.
For decades, scientists have thought that female mammals are born with a lifetime supply of oocytes, or female germ cells, already in their ovaries. That view was challenged last year by Jonathan Tilly, Joshua Johnson, and their colleagues at Massachusetts General Hospital in Boston. They reported in Nature that new oocytes could form throughout an adult mouse's lifetime (ScienceNOW, 10 March 2004). The research has not yet been repeated in another lab, and it still faces skeptics.
Tilly dropped another bombshell here this morning: He announced that he, Johnson, and their colleagues have found ovary-replenishing germ cells in the bone marrow and blood of adult mice. First, Tilly described finding genes typical of germ cells expressed in bone marrow samples from mice; he later mentioned that his team had found a similar pattern in humans.
Then, said Tilly, his team treated mice with two chemotherapy drugs that cause infertility, cyclophosphamide and busulfan. Mice that received the drug stopped producing new oocytes. But in mice that received bone marrow transplants, the scientists found oocytes in ovaries 2 months later. "The oocyte pool comes back," said Tilly.
The team saw similar results with genetically infertile mice. These animals have defects in a gene called ataxia-telangiectasia mutated. Almost a year after receiving bone marrow from healthy donors, the recipients' ovaries contained cells resembling oocytes. Tilly suggested that these results could explain reports of patients who give birth to children after receiving bone marrow transplants, despite prior treatments that normally destroy fertility. The research will appear later this week in Cell, said Tilly.
So far, however, Tilly's team hasn't proven that these cells can give rise to new offspring or that they undergo ovulation; it's also not known if the findings apply to other species. Scientists "need to do our homework and settle the matter once and for all," said David Albertini of Kansas University Medical Center in Kansas City, in a talk presented as a counterpoint to Tilly's. On the one hand, he said, "it's not too surprising that cells from the bone marrow would end up" in the ovaries of mice. A key question, noted Albertini, is "is it relevant to the process of reproduction?"
Society for the Study of Reproduction