In terms of infertility problems, the research may offer the most advantages, Brinster says. For example, males who are treated
with chemotherapy for malignancies, especially for boys in which there isn't sperm to save, may benefit. "In order to save
the germline of that individual, you might take a testis biopsy, grow it and expand it in vitro, and freeze the cells to eventually
re-implant them back into the male after the chemotherapy. In some infertility in humans and domestic animals there can be
stem cells present even in those animal's deemed infertile. It might be possible to expand those stem cells and use them in
a recipient to make sperm.
Brinster and other laboratories are working on a system for in vitro spermatogenesis, thereby eliminating a recipient that
is difficult to manage.
Applications for the use of stem cells seem as varied as the genome itself. Just looking at it from a reproductive vantage
point, the potential is enormous in creating healthier animals more resistant to disease. The serum-free culture media (stem
cells hate serum) is paving the way.
Scientific slight of hand
Here's how it worked: The research team identified a single growth factor: glial cell line-derived neurotrophic factor was
vital for promoting a signal-pathway that allowed the cells to multiply in culture. GDNF, originally identified as a survival
factor for neurons in the brain, was also found to be excreted by the Sertoli cells that surround and support the spermatogonial
stem cells in the testes. Once added to the culture, GDNF caused the stem cells to form dense clusters and proliferate continuously.
The researchers then used a gene marker, GFP, in the cultured stem cells to identify the cells before transplantation back
to infertile mice. These mice then produced offspring. The expression of the GFP gene made the mice glow green.
Editor's Note: Information for this story also provided by Greg Lester, University of Pennsylvania.