Researchers have found a way to directly convert spermatogonial stem cells, the precursors of sperm cells, into tissues of the prostate, skin and uterus. Their approach, described this month in the journal Stem Cells, may prove to be an effective alternative to the medical use of embryonic stem cells.
The hunt for alternatives to embryonic stem cells has led to some promising yet problematic approaches, some of which involve spermatagonial stem cells (SSCs). Researchers recently observed, for example, that SSCs grown in the laboratory will eventually give rise to a few cells that look and act like embryonic stem cells. This process can take months, however, and only a small percentage of the SSCs are converted into "embryonic stem-like" cells.
Other researchers have used viruses to insert genes into SSCs that will spur them to turn into ES-like cells. But this approach is problematic and the use of viruses to ferry in the needed genes has caused concern.
The new method, recently developed at the University of Illinois, takes advantage of the unusual interaction of two tissue types: the epithelium and the mesenchyme. The epithelium lines the cavities and surfaces of glands and many organs and secretes enzymes and other factors that are essential to the function of these tissues. The mesenchyme is the connective tissue in embryos. (In adults, the connective tissue is called stroma.)
In the 1950s, scientists discovered that the epithelium takes its developmental instructions from the mesenchyme. For example, when researchers put bladder epithelial cells on the mesenchyme of a prostate gland, the bladder cells were changed into prostatic epithelium. The prostatic mesenchyme had altered the fate of the bladder epithelium.
"The mesenchyme – it's the director; it's controlling the show," said University of Illinois veterinary biosciences professor Paul Cooke, who led the new study with postdoctoral researcher Liz Simon.
Cooke began the effort with what even he considered an unlikely proposition.
"Could we take spermatagonial stem cells and cause them to directly change into other cell types by putting them with various mesenchymes and growing them in the body?" he said. "I thought it was possible, but I didn't think it would work."