Scientists in China created the mice by fertilising normal mouse eggs with early-stage sperm cells that were manufactured from embryonic stem cells plucked from the animals. To make the sperm, the team nudged mouse stem cells through a complex series of steps known as meiosis that must be performed with extreme care to ensure the sperm develop properly. Study turns skin tissue from infertile men into early-stage sperm cells Read more Despite years of work, scientists have never managed to pull off the same trick with human stem cells, but the latest study could provide fresh impetus to the effort, said Jiahao Sha, director of the Laboratory of Reproductive Medicine at Nanjing Medical University in China. The creation of sperm and eggs - known as germ cells - for use in IVF raises particular safety issues, because any faults in their genetic material could harm not only the children born from the treatment, but all their future descendants. ?If it works, human germ cells could possibly be produced. However, in the current stage, ethics should be concerned, and any possible risks ruled out,? said Sha, who led the team The scientists believe that the cautious, stepwise production of the sperm cells was crucial for the mice to be born healthy and fertile. The mice went on to mate and have fertile offspring of their own, Sha said. Independent scientists welcomed the landmark achievement but cautioned that the creation of human sperm to treat infertile men was a distant prospect fraught with concerns over safety, ethics and legality. Advertisement Fertility clinics in Britain are banned from using artificial sperm or eggs to treat infertile couples. But if the procedure is ever perfected, MPs could come under pressure to revise the law. Instead of using stem cells, another promising approach aims to make sperm and eggs from adult skin cells. Infertility affects about 15% of couples and males are solely responsible for 20 to 30% of cases. One major cause of male infertility arises when the cells in the testes fail to divide to form proper, working sperm. While other groups have made sperm cells in the lab, Sha believes his is the first to make them according to agreed ?gold standards? and fully assess their quality. Writing in the journal Cell Stem Cell, Sha describes how he made early stage sperm cells - round, tailless cells known as spermatids - and injected them into mouse embryos. The fertilised embryos were transferred to females who bore at least six healthy mice. When these mice were old enough, they mated and produced a second generation of healthy babies. Mary Ann Handel, a scientist at the Jackson Laboratory in Maine who has written about the ?gold standard? milestones of sperm development, said: ?All this is of importance for basic science in reproductive biology. The implications for managing human infertility or onco-fertility are there, but I think they are considerably further off in the future. Of course, as for any exciting advance, the real ?gold standard? will be independent replication of this work by other groups.? Source: The Guardian