The bHLH transcription factor Olig2 promotes oligodendrocyte differentiation in collaboration with Nkx2.2

Olig2, a basic helix-loop-helix (bHLH) transcription factor, is expressed i n a restricted domain of the spinal cord ventricular zone that sequentially generates motoneurons and oligodendrocytes. Just prior to oligodendrocyte precursor formation, the domains of Olig2 and Nkx2.2 expression switch from being mutually exclusive to overlapping, and Neurogenins1 and 2 are exting uished within this region. Coexpression of Olig2 with Nkx2.2 in the spinal cord promotes ectopic and precocious oligodendrocyte differentiation. Both proteins function as transcriptional repressors in this assay. This effect is blocked by forced expression of Neurogenin1. By contrast, misexpression of Olig2 alone derepresses Neurogenins and promotes motoneuron differentiat ion. Olig2 therefore functions sequentially in motoneuron and oligodendrocy te, fate specification. This dual action is enabled by spatio-temporal chan ges in the expression domains of other transcription factors with which Oli g2 functionally interacts.