Japanese researchers have produced mouse eggs from stem cells that bred healthy offspring, a breakthrough that may one day help treat human infertility.
Researcher Mitinori Saitou and his team from Kyoto University in Japan used two different types of stem cells during their research: embryonic stem cells — a controversial technique since scientists must destroy embryos to cultivate them — and induced pluripotent stem (iPS) cells, which are adult cells, such as skin cells, that are reprogrammed to an embryonic-like state. Producing healthy eggs from iPS cells is potentially even more exciting than using embryonic stem cells, since iPS cells sidestep the ethical issues that plague those derived from embryos and because the resulting eggs would contain the same DNA as their donors.
Stem cell experts greeted the work with praise. “They’ve gotten to what was our Holy Grail, which is making eggs,” George Daley, a leading stem-cell scientist at Harvard, told NPR. “It’s like cellular alchemy. I mean, they can turn lead into gold here. They can turn skin cells or blood cells into eggs.”
In previous efforts, scientists — including the current group — have been able to create sperm and egg cells in the lab, but they weren’t able to produce healthy offspring from those cells. In the current study, published in the journal Science, the researchers first added growth factors and proteins to the stem cells to turn them into primordial germ cells. These cells were then combined with somatic cells from mouse ovaries to make “reconstituted ovaries,” which they transplanted into the mice. Four weeks later, the scientists removed them again, isolated immature egg cells from the ovaries and allowed them to mature in a dish. The mature eggs were fertilized with mouse sperm in a test tube and the resulting embryos were transferred into female mice, leading to the birth of healthy, fertile pups that went on to reproduce themselves.
It’s not at all clear whether the procedure would work similarly in humans, but the researchers if it does, it could revolutionize treatment for infertile couples and for older women who want children. “Now is the time for society to think about this,” Amander Clark, a stem cell scientist at UCLA, told the Los Angeles Times. “If we want to use stem cells to treat women who are older, we have to decide what the parameters are. Should this be available for women who are 40 to 50 years old? How about 50 and above? These shouldn’t be questions for scientists to decide alone.”
Indeed, such an advance would lead to a thicket of ethical questions: would you allow the use of tissues from a dead person to create new life, for example?
The researchers said the lab-created egg cells led to healthy pups less frequently than did natural mouse eggs, which were also fertilized and transferred to female mice in a control group. Mice impregnated with embryos created via in-vitro fertilization with natural eggs produced healthy offspring 13% of the time, compared with 3.9% for eggs created from embryonic stem cells and 1.8% for eggs made using iPS cells.
Nevertheless, the advance sheds light on how precursor cells eventually develop into sperm or egg cells, a scientific understanding that could in itself aid infertility treatments. That’s encouraging for the many women who struggle with fertility: according to the U.S. Centers for Disease Control and Prevention, about 10% of America women have problems getting pregnant or staying pregnant.