New eggs from bone marrow stem cells?
Dr. Kirsty Horsey
Progress Educational Trust04 August 2005
Bone marrow stem cells can produce new eggs in adult mice, US researchers say. A team based at Massachusetts General Hospital has shown that the eggs of mice rendered sterile with a drug can regenerate within 24 hours, and that these germ cells originate from bone marrow. The findings, published in the journal Cell, could help scientists develop new treatments for infertility or for delaying the onset of menopause.
The study builds on earlier work published by the group, which challenged the long-held belief that female humans, mice and other mammals are born with a finite supply of eggs. Jonathon Tilly and his colleagues found evidence of 'ovary stem cells' in mice - cells that are capable of producing fresh eggs throughout the animal's reproductive life. Initially, scientists thought that these stem cells must be present somewhere in the ovaries themselves. However, the new research indicates that stem cells found in bone marrow are producing germ cells that can 'home in' on the ovaries and start producing new eggs.
The researchers first showed that when they destroyed egg-containing follicles with the drug doxorubicin, hundreds of new eggs appeared within 24 hours. The team then identified germ cell 'markers' - proteins produced specifically by cells destined to become egg cells - in samples of mouse bone marrow. 'Everyone had missed finding female germline stem cells because they are not in the ovaries, where everyone would have looked for them', said Tilly.
The scientists also transplanted bone marrow from healthy mice into mice sterilised with two chemotherapy drugs, cyclophosphamide and busulfan. They found that new egg cells appeared in the ovaries of the treated mice one to seven days after transplantation, with egg cells still present 11 months later. The researchers got similar results when they transplanted bone marrow from normal mice into animals incapable of producing mature germ cells. Finally, they showed that the germline stem cells appear to travel from the bone marrow to the ovaries via the blood.
US fertility expert Kutluk Oktay said the study was 'rock solid evidence for the revolutionary concept that eggs can originate in bone marrow', adding that 'the most important follow-up study now is to confirm whether these eggs can resolve into pregnancies'. The scientists also found three germ cell markers in bone marrow and blood from women aged 23-36. 'This may launch a new era in how to think about female infertility and menopause', said Tilly. He said that in theory, bone marrow cells could be harvested from women and stored for twenty years. 'Then you put them back in, and they are going to do exactly what they are supposed to - find ovaries and generate new eggs', he added. Other experts welcomed the research, but cautioned that the findings need to be replicated.
Reproduced with permission from BioNews, an email and online sources of news, information and comment on assisted reproduction and genetics.