We evaluated p73 expression after BMP4 treatment of serum-deprived embryonal carcinoma P19 cells, known to upregulate Smad6 in response to BMPs.37 As depicted in Figure 6d, BMP-induced DNp73 levels, but not TAp73, correlated with increased levels of other BMP targets like Id1 or Smad6. Moreover, ectopic expression of DNp73 in serum-deprived P19 cells, enhanced BMP4-induced Id1 expression (Figure 6e, left panel) and prolonged Smad1/5/8 phosphorylation (Figure 6e, right panel). This evidence concerns the gene SMAD1 and embryonal carcinoma.