Oligodendrocyte Transcription Factor 1 (Olig1), Olig2 and Olig3 are basic-helix loop-helix (bHLH) transcription factors expressed in the motor neuron progenitor (pMN) domain of the spinal cord that generates motor neurons and oligodendrocytes. Olig1 is involved in the development and maturation of oligodendrocytes. Olig2 is required for oligodendrocyte and motor neuron specification in the spinal cord. Both Olig1 and Olig2 are expressed in the region of the ventral ventricular zone of late embryonic spinal cord where oligodendrocyte progenitors appear. Olig3 is transiently expressed in different types of progenitors of the embryonic central nervous system and then disappears in the course of development. In adults, expression of Olig3 is primarily detected in neural tissues.