Regionalization and fate specification in neurospheres: the role of Olig2 and Pax6

Neurosphere cultures are widely used to propagate multipotent CNS precursors, but their differentiation into neurons or oligodendrocytes is rather poor. To elucidate fate determination in this system, we examined the expression and function of candidate transcription factors in neurospheres derived from different CNS regions during development and adulthood. We observed prominent down-regulation of most transcription factors present in telencephalic precursors upon growth factor exposure in neurosphere cultures while Olig1 and Olig2 expression was strongly up-regulated. Interference with Olig2 in neurospheres revealed its role in self-renewal during expansion and for the generation of neurons and oligodendrocytes during differentiation. We further show that neurogenesis becomes fully Pax6-dependent in the neurosphere culture system, independent of the region of origin, and that Pax6 overexpression is sufficient to direct almost all neurosphere-derived cells towards neurogenesis. Thus, a pathway combining transcription factors of dorsal and ventral regions is activated in the neurosphere culture model.