Promotes formation and maturation of oligodendrocytes, especially within the brain. Cooperates with OLIG2 to establish the pMN domain of the embryonic neural tube (By similarity). Expressed specifically in the brain, including the corpus callosum, hippocampal and cerebral white matter. Also detected in cells scattered in gray matter, most probably in oligodendrocytes. Expressed in oligodendrocytes of the postnatal optical nerve up to day 30, then the number of expressing cells decreases. By SHH.