A team of German scientists reported today that it has succeeded in turning stem cells that become sperm in mice into cells with many of the characteristics of embryonic stem (ES) cells. If the same feat can be done with human sperm stem cells, scientists say the technique could offer a much-sought alternative to destroying human embryos for acquiring ES-like cells.
Spermatogonial stem cells, which continuously produce new sperm, are extremely hard to find in the testes. Only in 2004 did scientists finally succeed in growing such cells in culture from mice.
A team led by heart researcher Gerd Hasenfuss and Wolfgang Engel of the Georg-August-University of Goettingen in Germany, took the next step. Experimenting with various culture conditions, the researchers succeeded in producing colonies of stem cells exhibiting markers like those of ES cells. The researchers then attempted to see if the cells, which they labeled multipotent adult germline stem cells (maGSC), would differentiate into specific types of body cells. The answer was yes: They found cells with markers from all three major body cell types, called germ layers: ectoderm (such as nerve cells), mesoderm (muscle and blood vessel cells), and endoderm (kidney cells).
The researchers went on to see if the precursor cells would differentiate in live animals. They injected maGSCs into mice whose immune systems had been knocked out. Again, success. The mice grew teratomas, a kind of tumor that grows from germline cells and which contains many types of tissues. The scientists also injected dye-tagged cells into blastocysts, which they inserted into female mice. The introduced cells contributed to multiple organ systems in the offspring, the team reports online today in Nature.
Geneticist Robin Lovell-Badge of the U.K. Medical Research Council's National Institute for Medical Research points out that now "we have come full circle," since the field of ES research first arose from work on teratomas 40 years ago. Many scientists now say the big question is whether the work can be extended to humans. Ralph Brinster, part of the team at the University of Pennsylvania in Philadelphia that first cultured sperm stem cells in the lab, has written that culturing stem cells from human sperm is not far off--humans and mice, like other mammals, he says, require similar growth factors.
John Gearhart, a stem cell researcher at Johns Hopkins University in Baltimore, Maryland, says the study "appears to be the best so far" at offering a potential alternative to human embryonic stem cells.