Under this model, the loss of BMPR-II in the endothelium drives BMP9 signaling via alternative type-II receptors, such as ActR-IIa or ActR-IIb, resulting in prolonged activation of the canonical signaling pathway and a cancer-like shift of the BMP9 response towards pathological endothelial proliferation (Figure 2C). The gene discussed is GDF2; the disease is cancer.