Rethinking Reproductive Biology

Everyone knows that women are born with all the eggs they can ever make, right? Well, a recent study shows that everyone just might be wrong.

This doesn’t just change how we think about reproductive biology. It has real world implications for lots of infertile women too.

A woman makes all of her eggs while she is still in the womb. The way it works is that a group of cells called germ cells divides until they are nearly mature. These 400,000 or so cells then wait around until the woman is born and enters puberty. Then, around one cell per month matures and is released. By menopause, the average woman has released about 400 mature eggs.

Scientists thought for a long time that once ovaries made their batch of immature eggs, they lost this ability forever. They were mistaken. This study showed that a woman’s ovaries still have a few cells that retain their potential to become eggs.

These researchers not only identified these oogonial stem cells (or OSCs), but also managed to collect a few and to coax them into becoming immature oocytes in a petri dish. They then matured these immature oocytes in a mouse’s ovary. These scientists had created new eggs from cells found in a woman’s ovaries.

And they didn’t stop there. These scientists showed that mouse OSCs created the same way were capable of being fertilized and growing into healthy pups. The eggs made from these OSCs appear to be fully functional and like eggs in every way. (At least the mouse ones are.)

This changes how we think about egg biology. And more importantly, about how we might treat infertility in women in the near future.

Many women are infertile because there is something wrong with their eggs. Except in a few rare cases, this has meant that these women could not have children that shared their DNA. This new finding gives them hope.

If scientists can somehow get OSCs from an infertile woman, they will be able to turn it into an egg. Then a doctor would just follow the standard protocols of in vitro fertilization and nine months later, a baby.

Since these cells won’t be easy to get, an even better possibility would be to somehow encourage the cells into becoming eggs within the woman’s ovaries. Now she’d just be making eggs like she used to.

This might also help older women conceive. Older women’s eggs tend to have lower quality DNA which makes getting pregnant more difficult. If OSCs suffer less DNA damage, then perhaps this technique can be used to give older women a better chance at getting pregnant.