Olig genes are upregulated in oligodendrocyte precursor cells in the injured central nervous system

The Olig gene family encodes basic helixloop-helix (bHLH) transcription factors and plays a critical role in oligodendrogenesis during development. We examined whether the Olig genes are involved in pathological conditions such as the injured brain or spinal cord by in situ hybridization. Olig1 mRNA was detected in cells surrounding necrotic tissue. The signal intensity of Olig1 mRNA gradually increased 2 to 7 days and decreased by 14 days after injury. Olig2 mRNA was expressed in a similar pattern and was colocalized with Olig1 mRNA. Similar results were obtained for the expression of Olig1 and Olig2 mRNAs in spinal cord injury. When we compared the mRNA expression pattern of Olig1 with that of NG2 proteoglycan and platelet-derived growth factor receptor α (PDGFRα), markers for oligodendrocyte precursor cells (OPCs), by double labeling in situ hybridization, Olig1 mRNA was co-localized with mRNAs for NG2 proteoglycan and PDGFRα 7 days after brain injury, suggesting that Olig mRNAs were expressed in OPCs. These findings suggest that the Olig transcription factors regulate differentiation of oligodendrocytes in the injured CNS as well as in the developing CNS.