After being kept in culture for three months, the stem cells restored sperm production, and therefore fertility, in infertile mice. According to the researchers, this development will have profound consequences for future fertility therapies and provide a source of stem cells that will make it possible to modify genes from males before they are passed to the next generation. While the research was performed in mice, the researchers believe that it is likely applicable to other species, including humans.
"We've demonstrated that a central signaling process allows spermatagonial stem cells to continually renew themselves, essentially becoming immortal," said Ralph L. Brinster, a professor of reproductive physiology at Penn. "For research, this opens up a wonderfully robust diagnostic system for analyzing the function of individual genes. For medicine, it opens up a new chapter in fertility medicine." Spermatagonial stem cells and the hematopoietic stem cells that generate new blood cells are the only types of adult stem cells that can be positively identified using functional assays. It may also be possible to convert spermatogonial stem cells to totipotent cells, capable of becoming almost any other cell type and similar to embryonic stem cells.
Whereas the female germ cell, the egg, stops dividing before birth, the spermatogonial stem cells continue to divide throughout life. According to Brinster, it is possible to modify the male germ line between generations by manipulating the spermatogonial stem cells in culture.