Cross-repressive interaction of the Olig2 and Nkx2.2 transcription factors in developing neural tube associated with formation of a specific physical complex.

In developing neural tube, the basic helix-loop-helix (bHLH) transcription factor Olig2 interacts with the homeodomain transcription factor Nkx2.2 at two distinct stages. During neuronogenesis, a cross-repressive interaction appears to establish the precise boundary between the p3 and pMN domains. At later times, a cooperative interaction is noted because Nkx2.2 promotes maturation of oligodendrocyte progenitor cells specified by expression of Olig2. We show here that the Olig2 protein can form a physical complex with Nkx2.2 protein in mammalian cells and yeast two-hybrid trap assay. This interaction is specific because Olig2 does not bind to a biologically irrelevant homeodomain transcription factor (Nkx6.1), and Nkx2.2 does not interact with a biologically irrelevant bHLH protein (NeuroD). Deletion mapping analysis suggests that formation of an Olig2-Nkx2.2 physical complex is insufficient for the induction of oligodendrocyte progenitors in developing spine; however, the protein-protein interaction observed might be important for the cross-repressive interaction between Olig2 and Nkx2.2 that helps to establish the pMN-p3 boundary in the developing spinal cord.