Gotcha covered. A mouse glial cell (with dark-stained nucleus), derived from an embryonic stem cell, coats axons in a rat's spinal cord with myelin (brown stain).

Stem Cells as Potential Nerve Therapy

In the best example yet of the potential power of stem cells, a team of German and U.S. researchers has coaxed cells from mouse embryos to grow into apparently fully functional brain cells. The study, reported in tomorrow's issue of Science, reinforces the idea that stem cells--cells in an early stage of development that have not yet made a commitment to grow into a particular type of tissue--may be useful for treating diseases. But ethical and legal concerns about using human embryo tissue could stifle further research For their experiments, Oliver Brüstle of the University of Bonn Medical Center and his U.S. colleagues took cells from 3.5-day-old mouse embryos and coaxed them to grow and bunch together into embryoid bodies, a first step toward differentiation. Then the researchers cultivated the embryoid bodies in a medium that favors the survival of precursors to nerve cells and finally applied growth factors known to promote the proliferation of precursors to glial cells, a type of support cell in the brain that also produces myelin, an insulating sheath for neurons. Ultimately, the glial precursors formed the two major types of glial cells, known as oligodendrocytes and astrocytes. Five days later, the team detected the expression of CNP, a protein characteristic of the myelin sheaths of neurons, by the cells.

Earlier transplant studies had shown that oligodendrocyte precursors injected into animals suffering from myelin diseases had succeeded in coating the host animals' neurons. So Brüstle and his team transplanted their stem cell-derived oligodendrocytes into the brains and spinal cords of fetal and week-old rats that have the same mutation as humans with Pelizaeus-Merzbacher disease (PMD), a rare genetic disorder in which the myelin is defective. A few weeks later, the donor cells had generated numerous myelin sheaths on the rats' brain and spinal neurons. That suggests that similar transplants might help patients with PMD, which is usually fatal, or other demyelinating conditions.

Developmental biologist Davor Solter of the Max Planck Institute for Immunobiology in Freiburg, Germany, describes the work as "promising," adding: "It is nice that they put the pieces together and substantiated what everyone is believing"--that embryonic stem cells may have therapeutic uses. They might, for example, be used to treat people with multiple sclerosis or other conditions in which myelination is defective.

But such promise has prompted much soul searching on both sides of the Atlantic over current legislation banning embryo research. In the United States, current law forbids the use of public funds for deriving stem cells from human embryos. In Germany, restrictions are even tougher: Any research on or with human embryos is prohibited by law unless the embryo is the immediate beneficiary. And that doesn't seem about to change: In March, Germany's main research funding agency, the DFG, published a policy statement on research with human embryonic stem cells, which advised German policy-makers not to change the embryo protection law now.