Making Eggs from Scratch

Scientists Have Discovered a Special Type of Stem Cell in Ovaries that Can Produce More Eggs

We all learned in school that a woman is born with all of the eggs she'll ever have. Well, turns out the textbooks were wrong.

A new study published just last month shows that women's ovaries still have cells that can make new eggs. These cells are a type of those famous stem cells you've undoubtedly heard about in the news.  Scientists call these cells oogonial stem cells (OSCs) because they can develop into eggs, or oocytes.
What the study doesn't show is whether a woman ever actually uses these OSCs during her lifetime. But the scientists do show that they can use them to make mature oocytes in the lab. 
This will be a boon for researchers as they can now have an unlimited source of eggs for their research.  And it could turn out to be a Godsend for some infertile women. Women who are infertile because they have trouble making eggs might one day be able to have their own children using these newly discovered stem cells.

Making Eggs

Until just a few years ago, scientists thought that all of a woman's eggs were made while she was still in the womb. Before she's born, a certain group of cells called germ cells divides until they are almost mature eggs and then they stop. Once puberty hits, around one egg per month finishes maturing and is released.

When a woman starts to go through puberty, she has around 400,000 of these egg precursor cells. But in the end, only about 400 of these will ever become mature oocytes.
What this meant was that if something bad happened to a woman's eggs, she would not be able to have a baby. She had "all of her eggs in one basket," so to speak.
But turns out that nature is not as stupid as we thought! Adult women still have cells that can become new eggs.    
Scientists first had a hint that this was the case about 10 years ago. In 2004, a group of scientists from Harvard University discovered a set of germ cells in adult mouse ovaries that could become eggs. That's when they named these cells oogonial stem cells or OSCs.
These OSCs could become mature eggs in petri dishes and when injected into mouse ovaries. At the time, this news came as quite a shock, since no one up to this point believed that these cells even existed.
But scientists didn't know if the same thing happens in humans, too. After all, a mouse is not a person.
Then, after eight years of searching, the same group of scientists reported that they've identified OSCs in human ovaries. It took so long because there aren't a lot of these cells around in adults, and they are hard to tell apart from other cells in the ovary.
The first step was to find something that was different about OSCs to help distinguish them from all the other cells in the ovary. They settled on something that's known to only be on the outside of germ cells called Ddx4. They used this knowledge to go on a fishing expedition to isolate the OSCs.
Using an antibody that recognizes this label as bait, they were able to separate out any OSCs with Ddx4 on their surface from the rest of the cells in the ovary. They found that even though OSCs are pretty rare (they make up only about 1/100th of the ovary), they do actually exist.
Next, they wanted to show that these cells were actually OSCs. Just like the mouse OSCs, the cells were able to develop into mature oocytes in petri dishes and even inside mouse ovaries. 
But this wasn't easy either. To tell which cells were the OSCs that they added, the researchers used a common lab trick – adding green fluorescent protein or GFP.
GFP is what makes some jellyfish glow green. Scientists have found that they can pretty much get anything to glow green by adding this gene. This makes cells easy to follow...just look for the glowing green ones!
So by adding the gene for GFP to the OSCs, the scientists could follow the cells after they were injected into a mouse's ovary. They did this for OSCs that they isolated from mice and from humans, and found that both could develop into mature oocytes.
Then the scientists did something even cooler with the OSCs that they isolated from mice. After the mouse OSCs developed into mature oocytes in the ovary, they found that they could be fertilized. And the mouse pups that were born glowed green because they came from an OSC that had GFP in it!

More Information

Maybe women aren't born with all of their eggs in one basket.















A glowing protein helped scientists figure out which mice came from OSCs.

Using Stem Cells to Treat Infertility

You've probably heard of using stem cells to treat diseases like Alzheimer's and Parkinson's. If you understand what stem cells are, it makes sense that these are the kinds of diseases they might be useful for.

Stem cells are special because they can make more copies of themselves indefinitely. And more importantly for medicine, they can turn into many other kinds of cells.
This is different than most other kinds of cells in our body, which are stuck being what they are. For example, once a skin cell, always a skin cell.
Now you can see why stem cells are so exciting for treating diseases caused by dying cells. For example, scientists may one day be able to use stem cells to grow new brain cells for patients suffering from Alzheimer's or Parkinson's disease. Or new pancreatic cells for Type 1 diabetics. Or new nerve cells for people with spinal cord injuries. And the list goes on and on!
But you might not have thought of infertility. Female infertility can happen when a woman's ovaries don't produce good eggs, perhaps because of damage or aging. 
The current way to treat these women is to give them drugs or hormones that help their ovaries start producing better (and more) eggs. Or they can try in vitro fertilization. But these can be very costly and quite painful for the woman.
What if we could make eggs "from scratch" instead? The OSCs that were just found in human ovaries might make this possible. And this way, women could be treated for infertility with their own eggs instead of hormones.
Or even better, scientists might figure out how to get a woman's ovaries to turn OSCs into eggs without having to take them out. Then she can have a baby without in vitro fertilization or surgery.
But like other stem cell treatments, getting it to work is a lot easier said than done. Most stem cell therapies have only been around for 10 years or less. And most of these are still in experimental stages. So we still have a lot to learn about how the many different types of stem cells we have in our bodies can be used as medicine, but research is getting us closer everyday.
Dr. Maggie Pearce

Perhaps these new stem cell can help infertile women make new eggs like this one.