On September 20th, the journal Science published an article by Yamashiro et al titled:” Generation of human oogonia from induced pluripotential stem cells in vitro.” Oogonia are the cells that make eggs. Women generate 6- 7 million eggs while still in the womb, and no more after that (according to conventional thinking), so the production of new eggs could be a game changer…if this is indeed ‘ready for prime time’ use.
Oogonia are a type of stem cell. Stem cells are cells in the body that can make new cells. All humans start from the union of a sperm and egg to form an embryo which is a single cell. From that arise the trillions of cells that make a human. Stems cells are the cells responsible for creating the various different types of differentiated cells that are needed such as liver cells, muscle cells, brain cells etc. But once a stem cell starts to make a specific type of cells, brain cell for example, it loses the ability to revert and make a different type of cell. There is no ‘moonlighting’ when it comes to stem cells!
Since the body constantly needs regeneration of many cells type, stem cells are always needed. However, it has been thought that the ovary has no functional stem cells [oogonia] and thus once the eggs [oocytes] are formed and the stem cells are gone, the woman ceases to make new eggs. On top of that, women use their eggs at a rapid pace. A woman in her 20’s uses 1000 eggs per month no matter what she is doing. So, the egg pool becomes depleted, without being replenished, and at some point, there are no more eggs. This is when menopause occurs.
THE ROAD LESS TAKEN
Researchers have tried to get more stem cells so that a woman can continue to produce eggs. Two paths have been explored. One group of researches feels that there are some oogonia remaining in the adult ovary. If they could find these cells, they could expand them and create more oogonia to replace them in the women’s ovary. There is some research continuing here but the results have been slow and disappointing.
The other path is to use the procedure that led to the birth of “Dolly” where mature cells are reprogrammed to be stem cells and, in this case, oogonia. This is the path that the recent report pursued. In the human embryo at week two, human stems cells begin to produce proteins that distinguish them from other cells. By week five, the stem cells destined to produce eggs migrate to the area of the embryo that will eventually become the ovary. At week ten, these cells undergo a programming event, called epigenetic reprogramming, which commits them to make eggs.
NEWS FOR RODENTS?
The researchers took male stem cells and reprogrammed them by placing them with mouse embryonic ovarian cells. This was possible because cells that are destined to make sperm or eggs are very similar when they are less than ten weeks old. The technique used by these researchers did produce human oogonia like cells.
While this is a major step towards being able to produce new eggs, there is still a long way to go before these cells have been proven capable of generating a human. So, while not a breakthrough that can be used clinically today to cure menopause or age- related infertility, it nonetheless is another step towards that goal, with hopefully, more research and development to come.