In line with a role of Notch3 in tumour associated endothelial cells, we observed an increase in CD31 and DLL4 expression in tumours from Notch3LacZ/LacZ mice (Fig. 1b and supplementary Fig. 3b), but no change in αSMA or PDGFRβ (Beta-type platelet-derived growth factor receptor), two pericyte markers (Fig. 2b). The gene discussed is PECAM1; the disease is neoplasm.