Olig2 (211F1.1)

Olig2, a basic helix–loop–helix transcription factor, is involved in oligodendroglial specification. Olig2 expression has been reported in most glial tumors, such as oligodendrogliomas and astrocytomas1-2. Although more than half of glioblastomas are positive for Olig2, expression is very weak in terms of both percentage of labeled cells and intensity. No Olig2 expression has been found in the non-glial tumors including neuroepithelial tumors, ependymomas, subependymomas, medulloblastomas, and nonneuroepithelial tumors, such as CNS lymphomas, meningiomas, schwannomas, atypical teratoid/rhabdoid tumor, and haemangioblastomas1-2. Compared to the strong staining seen in glioma samples, a weak expression is observed in non-tumoral brain tissue (gliosis). In order to characterize cellular subtypes that constitute astrocytomas, oligoastrocytomas and oligodendrogliomas, double labeling of Olig2 and GFAP has been performed which identified two phenotypically distinct tumor populations. The first is Olig2+/GFAP– which has an oligodendroglial morphology, corresponding to pure oligodendrogliomas that contain only oligodendroglial cells; the second is Olig2–/GFAP+ which has an astrocytic phenotype, including not only oligoastrocytomas, but also WHO astrocytomas. Depending on proportion and spatial clustering of the two phenotypically distinct tumor populations, the tumor (Olig2-/GFAP+) is classified either as an astrocytoma when both populations are intermingled with a dominance of GFAP+ cells or oligoastrocytoma when there is some degree of spatial clustering of the GFAP+ cells.