What’s the News: Researchers at Kyoto University in Japan have created fully functioning sperm from mouse embryonic stem cells
. The sperm cells were able to fertilize mouse eggs in vitro, and when the scientists implanted the embryos into surrogate mothers, the mice gave birth to healthy offspring. The research, published in the journal Cell
, may someday help treat infertility in humans. What’s the Context:
Scientists have been trying for many years to create viable sperm and egg cells from embryonic stem cells, which can become any type of tissue in the body. In 2003, researchers succeeded in creating sperm-like cells, but the experiments could not produce successful pregnancies in mice. Other studies had similar results.
More recently in 2009, scientists at Newcastle University claimed to have created early-stage human sperm from embryonic stem cells. Many biologists doubted the research team’s results, and the study, which was published in the journal Stem Cells and Development, was later retracted after editors found that the scientists plagiarized a previous paper.
Also in 2009, researchers in the current study discovered a way to coax early embryo cells—called epiblast cells—to turn into primordial germ cells, the precursors to sperm and eggs. The technique involved induced signaling of BMP4, a protein long known to be required for the generation of germ cells.
How the Heck:
The researchers first created epiblast-like cells from a cocktail containing embryonic stem cells and several growth factors and proteins, which control cell proliferation, differentiation, and other activities. Then, using their method devised a couple years ago, they turned those epiblast cells into primordial germ cells.
The team injected the germ cells into the testes of sterile mice. When the researchers later removed the mice’s testes, they found that the germ cells had matured into normal-looking sperm. So, they used the sperm to fertilize mice eggs in vitro, and implanted the eggs into several female mice. The mice later gave birth to 65 healthy pups, which then had babies of their own.
The Future Holds:
There is still a long way to go before the work can be translated to people—the main hurdle will be figuring out how to make human sperm cells from induced pluripotent stem cells, which are often taken from adult skin cells and other tissue. The researchers were able to do this in their mouse study (and some mouse pups were born), but the process was a lot less successful than when they used embryonic stem cells.
The researchers also want to figure out how to transform the embryonic stem cells into fully functioning eggs, and how to develop sperm without using mouse testes.
Image courtesy of Gilberto Santa Rosa / Wikimedia Commons