Researchers in Japan have managed to produce mouse sperm from mouse embryonic stem cells (ES cells), according to a report in this week's advanced online publications of the Proceedings of the National Academy of Science. The research may prove valuable in the quest to understand and control male infertility.
In May 2003, the Japanese scientists reported that they were close to achieving this goal. Now, the scientists, based at the Mitsubishi Kagaku Institute of Life Sciences in Japan, say that they have actually produced normal, functioning mouse sperm. The scientists cultivated mouse ES cells with a protein called BMP4 that stimulates sperm cell development in an embryo. The resulting cells were allowed to grow in the laboratory before being transplanted into testicular tissue in host mice. Once in place, the natural body hormones of the mice caused the cells to progress through the final stages of sperm development.
Toshiaki Noce, leader of the research team, said that the sperm produced appears to be 'active' and that it has been used to successfully fertilise mouse eggs. Some cell divisions occurred in the fertilised eggs but, says Noce, further research must be done in order to determine whether they could develop fully-formed mouse fetuses.
Also in May 2003, a group of US-based scientists reported the first successful production of mouse eggs from stem cells in the laboratory. This means that, in theory at least, both eggs and sperm from mice can now be produced from ES cells. This development, speculates the Washington Post, may also apply to humans, as it seems that most things that work in a mouse model also work in humans. However, stem cell research is more advanced in mice, and it is likely that much more work will be required before it can be applied in humans.
Although it remains to be seen whether human egg and sperm cells could be produced from ES cells in this way, it seems that the new discovery may ignite some ethical debate. In theory, because egg cells were developed from both 'male' and 'female' ES cells, two men could have a biologically related child carried by a surrogate mother. But the sperm cells could only be produced from ES cells taken from male embryos, since they require the presence of a Y chromosome to develop, so the same would not apply to a female same-sex couple.