Fig. 1. Pro-BMP9 and pro-BMP10 are equivalent ALK1-ligands.

a Dose-dependent signalling assays in PAECs. Serum-starved PAECs were treated with different ligands at 2.48 pM (white bars), 8.27 pM (light grey bars) and 27.3 pM (dark grey bars) (using monomer molecular weight, equivalent to 0.03, 0.1 and 0.33 ng ml⁻¹ BMP9 GF-domain concentration) for 1 h. Changes in the ID1 gene expression were monitored using RT-qPCR. Data were presented as fold change relative to untreated cells, and means ± SEM of three independent experiments are shown. Source data are provided as a Source Data file. b–d Volcano plots comparing changes in global gene expression in PAECs after pro-BMP9 or pro-BMP10 treatment. Serum-starved PAECs were treated with 25 pM of pro-BMP9 or pro-BMP10 (purity can be found on SDS-PAGE with silver staining in Supplementary Fig. 8a, lanes 1 and 4) for 1.5 h before RNA was extracted for microarray analysis. Four different primary PAEC lines were used. Red dots above the dashed line represent the changes in target genes with adjusted p values of less than 0.05. Several representative target genes are highlighted in c and d. Full list of genes can be found in Supplementary Data 1 and 2. e Affinity measurements of BMP9 and BMP10 for ALK1 using Biacore. A CM5 Biacore chip was immobilised with ALK1 dimer (ALK1-Fc) or monomer (in-house purified ALK1 ECD, purity can be seen in Supplementary Fig. 8a, lane 7). The sensorgrams of BMP9, pro-BMP9, BMP10 and pro-BMP10 binding raw data (in black lines) were overlaid with a global fit to a 1:1 model with mass transport limitations (red lines). f A summary of kinetic parameters for ligand-receptor interactions derived from the Biacore measurements in e.