Fig. 9. Model of the role of ID proteins in mediating effects of BMP signaling. OLIG proteins bind to promoter regions after heterodimerizing with the E2A proteins, resulting in transcription of their downstream targets. In the presence of BMP4, all four ID proteins are induced, resulting in sequestration of OLIG 1/2 by ID2 and ID4 and of E2A proteins by all the IDs in the cytoplasm of progenitor cells. This inhibits OLIG binding to promoters of target genes, resulting in inhibition of OL development and enhancement of commitment to the astrocytic fate.