It is often said that females are on the clock when it comes to reproduction. They are believed to be born with a fixed amount of potential eggs suitable for reproduction, of which on average one is matured and released every month. Over time, these so-called oocytes decrease in quality, meaning that reproducing at relatively old age is not recommended, as it may lead to birth defects or spontaneous abortions. However, a recent genetic study tracking certain special cells in the ovary reveals that females seem to produce potential eggs during life after all.
Stem cells
In the ovaries, special 'precursors' known as oogonial stem cells are thought to generate oocytes, which are released monthly and form the typical eggs necessary for fertilization and reproduction. It is thought that these stem cells divide themselves in order to create new, immature oocytes, but only do so before birth. Thereafter the precursor cells have themselves specialized into oocytes, and no further generation of potential eggs is possible.
New theory
Scientists from the University of Edinburgh and Massachusetts General Hospital looked at how often these oogonial stem cells divided, as observed by assessing their genetic profile. They used a tool to link genetic information to the number of cellular divisions in mice. By doing that, the researchers found cellular divisions taking place during life, while one would typically expect that all divisions were complete prior to birth.
Outlook
It is clear that much more research is needed, as the scientists only did a genetic analysis, and did not demonstrate their findings in humans. Future studies should be aimed at finding actual cellular division inside ovaries, revealing that the genetic findings correspond to physiology. Nevertheless, the study challenges the traditional views that no new oocytes can be produced during life, leaving women with a fixed and expendable source of eggs. Despite these findings, the evidence that reproducing at relative old age is not recommended still stands, indicating that ageing is a problem regardless of any oocyte production during life.
Stem cells
In the ovaries, special 'precursors' known as oogonial stem cells are thought to generate oocytes, which are released monthly and form the typical eggs necessary for fertilization and reproduction. It is thought that these stem cells divide themselves in order to create new, immature oocytes, but only do so before birth. Thereafter the precursor cells have themselves specialized into oocytes, and no further generation of potential eggs is possible.
New theory
Scientists from the University of Edinburgh and Massachusetts General Hospital looked at how often these oogonial stem cells divided, as observed by assessing their genetic profile. They used a tool to link genetic information to the number of cellular divisions in mice. By doing that, the researchers found cellular divisions taking place during life, while one would typically expect that all divisions were complete prior to birth.
Outlook
It is clear that much more research is needed, as the scientists only did a genetic analysis, and did not demonstrate their findings in humans. Future studies should be aimed at finding actual cellular division inside ovaries, revealing that the genetic findings correspond to physiology. Nevertheless, the study challenges the traditional views that no new oocytes can be produced during life, leaving women with a fixed and expendable source of eggs. Despite these findings, the evidence that reproducing at relative old age is not recommended still stands, indicating that ageing is a problem regardless of any oocyte production during life.
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| Image of an egg cell, taken with an electron microscope. |
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