No mature eggs from bone marrow

Mature ovulated mammalian eggs can't arise from circulating stem cells, according to a report in this week's Nature. The study questions the physiological relevance of putative regenerated oocytes another group had reported in a 2005 Cell paper, but does not directly refute those findings, the authors say."I don't think the results are contradictory, because the endpoints are different," said Nature study co-author Amy Wagers, of Harvard University. The previous work examined immature oocytes in the ovary, while the current paper analyzes ovulated eggs ready for fertilization. But the cells seen in the earlier studies "are not likely to be available for fertilization and they're not likely to contribute to female fertility," she added. "There's no definitive proof of what those cells actually do."Cells circulating in the blood may express markers found in germ cells, said lead author Kevin Eggan, also of Harvard, "but I think I...