Scientists have found evidence that adult women have stem cells in their ovaries that let them generate more eggs, challenging the long-standing belief that women are born with a fixed number of ova.
In a study published in the journal Nature Cell Biology, Chinese researchers performed experiments on mice, showing for the first time that a mammal can produce new eggs as an adult that lead to healthy offspring, reports theWashington Post. Scientists from Shanghai Jiao Tong University identified female germ line stem cells in ovaries removed from mice. After coaxing the cells to multiply, they were injected into sterile mice. Some of the cells matured into eggs, and another group of mice was able to produce healthy offspring.
While men produce new sperm daily, for at least 50 years scientists have believed that female mammals are born with all the eggs they will ever have and the supply is depleted over time, leaving them infertile after menopause. The new study raises new possibilities for the treatment of infertility, as freezing stem cells may be more efficient than freezing eggs and there may be ways to stimulate the cells to produce eggs in older women. The cells may also have a use in stem cell research by producing embryonic stem cell lines specific to individual patients.
Several recent studies have suggested that women may generate more eggs during adulthood, but this is the first time scientists have obtained the cells that can produce healthy new eggs from a mammal. "If you are looking to disprove that females cannot make new eggs, this paper proves it. It's a really significant paper," said Harvard Medical School professor Jonathan L. Tilly, who published some of the earlier research. "This is the smoking gun."
Other scientists say more research needs to be done on humans, not mice, and question if the mice used in the experiment were really completely sterilized. "The aging process of the human egg differs fundamentally from that of the mouse egg," said David L. Keefe, a professor of obstetrics and gynecology at the University of South Florida. "Except at Disney World, humans are not large mice."
Still, doctors hope that the cells could lead to new procedures someday, especially since treating infertility has become a lucrative, multibillion dollar business. The L.A. Times reports that the competition became so intense at the Huntington Reproductive Center in Pasadena, one of the biggest fertility practices on the West coast, that it has spurred a series of lawsuits. After founder Dr. Joel Batzofin's business grew to make a $5 million yearly profit, his five partners took a secret vote and ousted him from the business. The former partners sued each other in a six year legal battle that led to private detectives posing as patients. A female detective submitted to an ultrasound of her uterus and ovaries, and one of the doctors gave his own sperm sample to a rival doctor, pretending to be a patient, all in an effort to show that Batzofin was violating a non-compete agreement at his new practice. "It's a cutthroat business," said Batzofin. "There is a lot of greed."
But according to another new study published this week, even more women may be turning to fertility treatments, as having a high-powered career has supposedly been linked to lowered fertility. The Times of London reports that University of Utah anthropologist Elizabeth Cashdan found that women with stressful careers experience a hormonal shift that replaces estrogen with male androgens that are associated with strength, stamina, and competitiveness.
Cashdan analyzed the waist to hip ratio (WHR) of women from 37 different populations and cultures, and found the average WHR to be above 0.8. She says that due to a hormonal shift, the women had a more straight-up-and-down figure that is less conducive to child-bearing. Previous studies have found that women with an hourglass figure, with a WHR of 0.7 are the most fertile.
"Although the hormonal profile associated with a high WHR may favour success in some stressful and difficult circumstances where women must work hard, there are well-known costs," said Cashdan. "Women may suffer lower fertility and possibly lower attractiveness to men who may have an innate preference for curviness."
A Possible Step Toward Setting The Biological Clock [The Washington Post]
Fertility Doctors' Competition Spawns Lawsuits [The L.A. Times]
Is Your Career Making You Infertile? [The Times of London]