In an illustration of the unexpected twists science can take, German scientists have found that a type of cell called a spermatogonial stem cell from the testis can be coaxed to behave as a generalized or multipotent stem cell at least in mice. In testis, these cells are what in biology are called "germ cells", that is specialized diploid cells capable of undergoing meiosis and development into gametes.
Image: Slide of spermatogenesis in Grasshopper. Note the sperm bundles.
In males these germ cells are called spermatogonia. Of course we don't know if the corresponding cells in humans have the same flexibility. This research is exciting to some people because it seems to get around the ethical issues posed by harvesting embryonic stem cells. We shall see. But right now it looks like a simple scientific discovery might remove one of the big ethical objections to using stem cells.
I wonder if either germ cells or primary oocytes in females can be used in the same way. Of course this might be difficult since the female's germ cells are found in the fetus and female germ cells don't under go the sort of continuous production that male germ cells do.
Other links:
Stem cells found in adult mouse testes.
http://www.nature.com/news/2006/060320/full/060320-10.html
Testicles may provide a better kind of stem cell. http://www.timesonline.co.uk/article/0,,13509-2102393,00.html
Mice cells mimic embryonic stem cells.
http://www.cnn.com/2006/TECH/science/03/24/stem.cells.reut/index.html?eref=yahoo
Comparison of spermatogenesis and oogenesis.
http://www.uoguelph.ca/zoology/devobio/210labs/meiotbl.
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