New research from the University of Gothenburg in Sweden appears to rule out the possibility that ovarian stem cells exist. This is a direct contradiction of previous research released in February from Massachusetts General Hospital, which concludes that stem cells could be harvested from a woman's ovaries and morphed into functional eggs.
New Scientist reports on the finding by lead researcher Kui Liu and his team, which is published in the Proceedings of the National Academy of Sciences.
New Scientist notes, not surprisingly, that scientists are split on the validity of Liu's research. Hugh Clarke at McGill University in Canada, for example, told the publication that he was impressed with Liu's study and that it was "carefully done." But Jonathan Tilly, a reproductive biologist at MGH who led the previous work that affirmed the existence of ovarian stem cells, said he stands by his finding and that Liu's team could have spotted stem cell development with longer monitoring of the cell samples. Evelyn Telfer from the University of Edinburgh in the U.K., agreed, telling New Scientist that Liu's findings don't preclude the notion of the existence of ovarian stem cells and that Liu's finding is dubious because it is not an "apples to apples" comparison with Tilly's approach.
Tilly and his group produced their signature finding after looking for human ovarian tissue with vasa on the surface. Vasa protein is crucial, because as the cells Tilly and his team identified as ovarian stem cells in mice mature, vasa is pulled from the surface of the cell into the center. As New Scientist recaps, Tilly's group identified these cells as stem cells because after injecting the human equivalent into a small piece of ovarian tissue that was grafted under mice's skins, the cells subdivided into immature eggs over a period of two weeks.
Liu's study looked at the issue differently, as New Scientist explains. First, the team started with a mouse genetically modified to make its cells glow green. This mouse was then bred with a transgenic mouse that carried a portion of DNA that recognized vasa and subsequently changes the color of cells carrying the protein. The mouse offspring had green cells overall, and blue, yellow or red vasa cells, according to the story. Over three days, Liu monitored the cells that were not green. After injecting these cells into a section of mouse ovary, the process never led to the creation of eggs.
Liu's argues that while the cells may look like stem cells, they behave differently. He told New Scientist that "we're not even sure" what those cells are. Let the debate continue.
- read the New Scientist article
- check out the PNAS abstract