Selective expression of Nkx-2.2 transcription factor in chicken oligodendrocyte progenitors and implications for the embryonic origin of oligodendrocytes

Recent studies have demonstrated that oligodendrocytes originate from the v entral region of the developing spinal cord. However, the precise neuroepit helial origin of oligodendrocytes remains controversial, and the transcript ional control of oligodendrocyte lineage specification is largely unknown. Here we present evidence that oligodendrocytes in the embryonic chicken spi nal cord can be generated from neuroepithelial cells that express the Nkx-2 2 homeodomain transcription factor. Nkx-2.2 expression is initially confine d to a narrow stripe of neuroepithelium flanking the floor plate. Later, Nk x-22+ cells migrate ventrally and dorsolaterally into the surrounding gray and white matter regions where they undergo rapid proliferation. Double lab eling experiments revealed that Nkx-2.2+ cells coexpress markers specific f or oligodendrocyte progenitors, e.g., PDGFR alpha+, O4, and R-mAb antigens. In the brain, the Nkx-2.2 cells are also highly migratory and can generate oligodendrocytes. The persistent expression of the Nkx-2.2 homeodomain tra nscription factor in the oligodendrocyte lineage suggests its important rol e in the control of oligodendrocyte development.