Ovarian Stem Cells Give Birth to New Hope for Infertility Sufferers
Textbooks and 50-year-old dogma state that females are born with all the eggs that they will ever have. However the discovery of stem cells in human ovaries brings forth the possibility that new eggs are actually produced throughout life. The premise of limitless eggs implies new possibilities for increasing the chances of fertility for millions of women.
In the female fetus it is believed that oogonial stem cells (OSC) expand mitotically and then oocytes (reproductive cells) form. The oocytes undergo cell division (meiosis), but they are arrested in the first stage of division. thus there are no remaining OSC’s, but a large population of oocytes that remain in stasis until puberty, where one oocyte completes meiosis to form an ovum during each menstrual cycle. Since no OSC remain to stimulate oocyte growth, the oocytes decrease in number until there are no more left, marking the end of reproductive capacity of the woman (for a more in-depth explanation http://njms.umdnj.edu/gsbs/stemcell/scofthemonth/2008/GSCsci.html) . The new research by Jonathan Tilly and colleagues at Massachusetts General Hospital in Boston challenges this idea through their findings that whilst numbers of oocytes decrease over time, within the period it took for the total cell numbers to drop to 500, 1500 cells were dying, suggesting that new cells were being made at the same time. Many important proteins hormones exclusive to OSC’s were identified amongst the cells, supporting TIlly’s claims.
The team singled out the cells expressing this protein and tagged it with a glowing fluorescent protein making the cells glow green to make them more identifiable, then they implanted these cells in human ovary tissue and grafted in under the skin of a mouse. It was found that these cells were able to form multiple new eggs as they interacted with the other reproductive cells in the ovary tissue creating the follicles that have the potential to form embryos. This suggests that the cells may not be stuck in meiosis after all.
OSC stimulated oocyte developing and dividing.
These findings have stirred some enthusiasm amongst the scientific community, getting gynecologists excited about new possibilities to assist patients suffering from fertility issues.
Current limitations to IVF revolve around the inefficiency of the process as the repeated and expensive rounds of hormone therapy involved coupled with egg extraction, usually only supplies around 7 eggs at a time. Alternatively Tilly believes that all the eggs necessary for IVF could be harvested from one small piece of ovary containing the OSC’s. Tilly explains that “"From a 3-millimetre piece of tissue we can get 100 [stem] cells," he says. "We can make a million of those cells in culture and each has the potential to make an oocyte." Furthermore there is the possibility of rejuvenating older and damaged eggs. One example can be found in cancer patients where ovarian tissue is often extracted and frozen in order to preserve eggs from the harmful effects of chemotherapy. This process creates problems as the tissue may still contain cancerous cells, thus the extraction of individual stem cells with the potential to create oocytes could create a more conservative and reliable method. What’s more, older oocytes can be rejuvenated through the addition of the mitochondria from the stem cells to add new energy to older cells to assist in creating error-free cell division.
These new discoveries challenge old theories and create many new possibilities in the study of reproductive biology. Hopefully giving women with fertility issues new hope.
Hamzelou, J. (2012, February 26). Ovarian stem cells discovered in humans . Retrieved March 15, 2012, from New Scientist: http://www.newscientist.com/article/dn21517-ovarian-stem-cells-discovered-in-humans.html?full=true
Tilly, J. L. (2004, March 11). Germline stem cells and follicular renewal in the postnatal mammalian ovary. Nature , pp. 145-150.
Yvonne A R White, D. C. (2012, February). Oocyte formation by mitotically active germ cells purified from ovaries of reproductive-age women. Nature Medicine , pp. 413–421.