Fig. 2. BMP4 decreases expression of OL transcription factors and increases expression of ID genes. (A) Expression of mRNAs for Olig1, Olig2, Nkx2.2 and Sox10 was analyzed by quantitative RT-PCR performed with mRNA extracted from E17 progenitor cells grown in absence (blue) or presence (red) of 20 ng/ml BMP4 for 2, 8 and 35 hours. BMP4 treatment did not reduce levels of the transcripts until 8 hours. However, by 35 hours all transcripts were reduced by as much as 60-fold. (B) Expression of Id2 and Id4 mRNAs was analyzed by quantitative RT-PCR performed with mRNA extracted from E17 progenitor cells grown in absence (blue) or presence (red) of 20 ng/ml BMP4 for 2, 8 and 24 hours. Id4 and Id2 transcripts were both induced by BMP4 at 8 hours and subsequent time points. Graphs shown are representative of experiments done in duplicate three times. (C) Western blot analyses were performed to detect ID1-4 proteins using cell lysates from E17 progenitor cells grown in the absence (control) or presence of BMP4 for 12 hours. BMP4 treatment increased the expression of all the ID proteins.