Embryonic stem cells from mice can spontaneously form the precursors of sperm in a culture dish, scientists report this week. When the immature cells are inserted back into mouse testes, they can develop into mature sperm. The work should help researchers better understand the molecular cues that control the formation of germ cells, but worried bioethicists can breathe a sigh of relief: Artificial sperm factories are not on the near horizon.
Embryonic stem (ES) cells are derived from early embryos and can in theory become any cell in the body. But scientists are still piecing together the cues that trigger various cell types to form. A few months ago, researchers reported that oocytes can form spontaneously in colonies of mouse ES cells (ScienceNOW, 1 May), the first demonstration that ES cells can form germ cells in vitro. But forming sperm turns out to be a slightly more complicated task.
The first step, for Toshiaki Noce of the Mitsubishi Kagaku Institute of Life Sciences in Tokyo and his colleagues, was to engineer stem cells to glow with green fluorescent protein when a gene specific to developing sperm is turned on. In a paper published online this week by the Proceedings of the National Academy of Sciences, the researchers report that when they allowed the ES cells to form clusters of differentiating cells called embryoid bodies, a few of the cells glowed green, suggesting that they were expressing sperm-specific genes. When the scientists rounded up the green cells and inserted them into host mouse testes, some of the cells matured into sperm.
The scientists do not yet know whether the sperm can successfully fertilize an egg. If so, it might provide a new method to produce genetically modified mice. But researchers won't be able to make vats of sperm in the lab anytime soon, Noce says. Unlike oocytes, he says, immature sperm "are totally dependent on supporting cells in the testes," an environment that's very difficult to re-create.
The study will nevertheless help scientists to learn more about the molecular processes that control the formation of both sperm and oocytes and could lead to a better understanding of infertility, says Anna Wobus of the Institute of Plant Genetics and Crop Plant Research in Gatersleben, Germany.
Mitsubishi Kagaku Institute of Life Sciences