Researchers at the ASHBi Institute for Advanced Research in Human Biology in Kyoto, Japan, have demonstrated the development of functional sperm in mice that develop into fertile offspring from pluripotent embryonic stem cells. This is the first study to recover functional sperm from mouse pluripotent stem cells in vitro. This opens up new possibilities for the differentiation of male germ cells. This study used mouse embryonic stem cells that had been induced to form cells similar to primordial germ cells. The resulting sperm had no tails, but by injecting spermatids, they were able to fertilize an egg and create embryos that resulted in viable fertile offspring.