FGF-dependent generation of oligodendrocytes by a hedgehog-independent pathway

During development, spinal cord oligodendrocyte precursors (OPCs) originate from the ventral, but not dorsal, neuroepithelium. Sonic hedgehog (SHH) has crucial effects on oligodendrocyte production in the ventral region of the spinal cord; however, less is known regarding SHH signalling and oligodendrocyte generation from neural stem cells (NSCs). We show that NSCs isolated from the dorsal spinal cord can generate oligodendrocytes following FGF2 treatment, a MAP kinase dependent phenomenon that is associated with induction of the obligate oligogenic gene Olig2. Cyclopamine, a potent inhibitor of hedgehog signalling, did not block the formation of oligodendrocytes from FGF2-treated neurosphere cultures. Furthermore, neurospheres generated from SHH null mice also produced oligodendrocytes, even in the presence of cyclopamine. These findings are compatible with the idea of a hedgehog independent pathway for oligodendrocyte generation from neural stem cells.