www.newscientist.com/news/news.jsp?id=ns99994765
Male mammals continually produce sperm from a store of stem cells. But since the 1950s, biologists insisted that no egg stem cell source existed in adult female mammals, so that a woman only has the eggs she was born with. The numbers simply decline until the menopause, when the supply is exhausted. For example, when biologists opened mouse ovaries and counted the number of healthy follicles - the tiny sacs in which eggs grow - they found the number declined slowly with age. Jonathan Tilly says his team at the Massachusetts General Hospital in Boston took a different approach because they studied atresia, the process by which the follicles die. They discovered that follicles were dying so rapidly in mouse ovaries that the egg supply should have been depleted in a few weeks, even though female mice are fertile for more than a year. Text book Since the number of living follicles dropped much more slowly, that suggested - contrary to every text book on reproductive biology - that new egg follicles were being created well into adult life from stem cells. After a few weeks, the implanted ovary grew new follicles, containing the glowing protein. Stem cells from the modified mice had infiltrated the transplant and formed new eggs. If such stem cells exist in women, they could provide a way to treat infertility problems, such as the destruction of eggs during cancer chemotherapy.
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