Hiroshi Kubota, DVM, PhD, and colleagues report their findings this week in an online edition of the journal Proceedings of the National Academy of Sciences.
The researchers, who work at the university's school of veterinary medicine, conducted their experiments with sperm stem cells from mice. However, the same principle may also work with human sperm stem cells, say the researchers in a news release.
Sperm stem cells can't actually fertilize an egg. Instead, they give rise to cells that develop into sperm cells that then do the job of fertilization.
Stem cells such as these are called adult stem cells and are not the same as embryonic stem cells.
Kubota's team worked to develop a fluid mixture in which sperm stem cells could grow in large amounts, reproduce themselves, and survive outside the body. They needed to find the right combination of key ingredients called growth factors that would nurture the stem cells.
The researchers succeeded in getting the "recipe" right that would allow these cells to reproduce themselves. They took sperm stem cells from mice and added a gene to help identity the stem cells once transplanted.
Offspring of the mice who received the transplanted stem cells carried the extra gene, which had no purpose except to show that the implanted sperm stem cells worked.
The technique has many possible applications.
As in the mice experiment, genetic changes to sperm stem cells are passed on to the sperm, and, eventually, to any offspring produced from those sperm.
Freezing sperm stem cells could also preserve them indefinitely. One day, that may let men save their sperm stem cells for future use, which could help men facing chemotherapy preserve their fertility.
Currently, men facing infertility from chemotherapy can store their sperm before treatment. However, those sperm don't always yield children later on; the pregnancy success rate for frozen sperm is less than 50%, according to a news release.
Likewise, sperm stem cells of boys needing chemotherapy could be cultured to increase their numbers and then preserved for the boys to use when they grow up and want to have children.
Preserving sperm stem cells could also help enhance survival of endangered species of animals or valuable livestock, says the news release.