The early-stage embryos were successfully transplanted into the female mice which produced seven babies. Six developed into adult mice.
The work was funded by the University of Gttingen and the Germany Research Council (DFG).
Prof Nayernia, who originally hails from Shiraz in Southern Iran, said: "This research is particularly important in helping us to understand more about spermatogenesis, the biological process in which sperm is produced. We must know this if we are to get to the root of infertility.
"If we know more about how spermatogonial stem cells turn into sperm cells, this knowledge could be translated into treatments for men who are unable to produce mature sperm, although this is several years down the line. For example, we could isolate a patient's spermatagonial cells using a simple testicular biopsy, encourage them in the laboratory into becoming functional sperm and transplant them back into the patient."
The findings could also inform a field of stem cell research known as nuclear transfer, or therapeutic cloning, which aims to provide tailor-made stem cells to aid disease therapy and infertility. Sperm cells could potentially be created using this method.
Prof Nayernia and his team in Germany were the first in the world to isolate spermatagonial stem cells. The team was also able to show that some of these stem cells, called multipotent adult germline stem cells (maGSCs), turned into heart, muscle, brain and other cells.
Although previous studies have shown that embryonic stem cells grown in the laboratory can become germ cells that give rise to cells resembling sperm cells or gametes, this is the first time scientists have tested whether the gametes really work in real life.
Prof Nayernia added: "Spermatogonial stem cells are extremely promising and more research is
Contact: Claire Jordan
University of Newcastle upon Tyne