Potent circulating inhibitor of angiogenesis. Signals through the type I activin receptor ACVRL1 but not other Alks. Signaling through SMAD1 in endothelial cells requires TGF-beta coreceptor endoglin/ENG. {ECO:0000269|PubMed:18309101, ECO:0000269|PubMed:21710321, ECO:0000269|PubMed:22799562, ECO:0000269|PubMed:23300529, ECO:0000269|PubMed:25237187}. This is the function of GDF2 (growth differentiation factor 2, Ensembl gene identifier ENSG00000263761).