1096 The Journal of Cell Biology

Making more brain dults make new brain cells. But where do those nerve cells come from? New findings suggest that a subpopulation of glia—the brain’s filler material—act as the all-important neuronal precursors. Even more startling, a widespread glial cell type called the astrocyte can be converted into a neuronal precursor by the expression of a single gene. “These astrocytes are not viewed anymore as a specialized cell type but rather as a precursor cell, ” said Magdalena Götz (Max-Planck Institute, Göttingen, Germany). “And once we think we have precursors everywhere, we can think how to manipulate these precursors.” Precursor activity is most obvious in the developing brain. In the neocortex, for example, it was thought that newly born neurons migrated up the long processes of radial glial cells. Bu