No fertilizable oocytes from blood stem cells
Researchers at the Joslin Diabetes Center have not been able to find any evidence that cells present in the blood or bone marrow migrate into the ovary and form ova capable of ovulation and thus making them available for fertilization. In doing so, they contradict the conclusions of a study that aroused this very hope last year.
Jonathan Tilly from Massachusetts General Hospital and his colleagues reported for the first time in 2004 that the supply of oocytes in mice is not limited, as previously assumed, but can continue to be increased over the course of life [1]. Initially, they suspected that the origin was stem cells capable of further division at the edge of the ovaries, then in July 2005 they reported on hematopoietic stem cells that had migrated into the ovaries via the bloodstream and were now maturing there into egg cells. If they injected blood from non-sterile conspecifics into sterile mice, they were soon able to detect newly formed germ cells in the ovaries [2]. However, these results are highly controversial in the professional world and have not yet been independently confirmed.
Amy Wagers and her colleagues have now found that cells circulating in this way at least do not lead to eggs capable of ovulation. The researchers had coupled the bloodstreams of two mice each. Since the cells of one of the two animals also produced green fluorescent protein, the scientists were able to follow the fate of individual cells in the common circulation. When they stimulated ovulation with hormones, they found no egg cells in the individual animals whose progenitors originally came from the other: i.e. no green glowing in the non-glowing specimen and vice versa. They also could not find any positive effect if they sterilized one of the two animals beforehand with chemotherapy: Despite the influx of possible stem cells with the blood of the coupled animal, the infertile rodents continued to show impaired fertility after the treatment [3].
One of the hopes fueled by the results of Tilly and his colleagues was that simple blood transfusions could restore fertility to women with impaired ovulation or after chemotherapy. Wagers and her colleagues consider this to be wrong given their results.
