Transplanted NG2 + cells (green) become functional inhibitory interneurons.

The brain is a rapidly changing landscape. After birth, its alterations require a source of progenitors that can form different cell types. In an attempt to characterize these progenitors, Aguirre et al. (page 575) have identified a population of neural stem cells (NSCs) that make inhibitory neurons in the postnatal mouse brain.

Neurogenesis is common in an area of the brain known as the subventricular zone (SVZ), so this seemed like a likely place to find NSCs. The same laboratory had previously shown that cells expressing the NG2 proteoglycan, once thought to give rise only to oligodendrocytes, could form active neurons in vitro. They now find that a portion of NG2-expressing cells that reside in the SVZ are these NSCs, which contribute to neurogenesis in the postnatal brain.

Some of the SVZ NG2+ cells also expressed proteins that mark stem cell populations. These cells were the progenitors of hippocampal neurons. The group isolated NG2+ cells from the brain of one mouse and transplanted them into the lateral ventricle of a host mouse. Weeks later, progeny of the transplanted cells that ended up in the white matter had formed oligodendrocytes. But those that found their way to the hippocampus had become fully functional and integrated inhibitory interneurons.

The inhibitory neurons formed by NG2+ NSCs are the same type of cells that degenerate in a common childhood form of epilepsy. The next step is to determine whether transplanted NG2+ cells can regenerate these lost neurons in a mouse model of the disease. ▪