Working with three of WiCell's five human embryonic stem cell lines, Xu and his team explored the molecular interactions within the stem cell growth medium. He discovered that, in certain conditions, a protein known as fibroblast growth factor 2 (FGF2) accomplishes the same critical role that feeder cells are thought to play: ensuring that the stem cells remain in their undifferentiated state and capable of proliferation.
"We've got it down to the mechanism," Xu says.
Moreover, Xu made the surprising discovery that the very molecules that encourage human embryonic stem cells to differentiate appear to inhibit differentiation in mouse embryonic stem cells.
Aside from feeder cells, two other sources of animal material remain in stem cell culture materials. One, Matrigel, is a product that is essentially a plate-coating matrix of cells extracted from mouse tumors. Serum replacement, which is bovine in origin, is the other animal material still needed to culture stem cells.
Xu became interested in unveiling molecules derived from the mouse feeder cells because, in their absence, stem cells start to differentiate within two to three days. Xu started by evaluating the effect of changing stem cell growth conditions - using less feeder cell material, or no serum replacement, for instance.
Unexpectedly, Xu found that the presence of serum replacement promoted stem cell differentiation. Digging deeper, he found that serum replacement mimics the activity of bone morphogenetic protein (BMP), a molecule known to kick-start embryonic development, or in this case, cell differe
Source:University of Wisconsin-Madison