Vascular endothelium glycoprotein that plays an important role in the regulation of angiogenesis (PubMed:10625534). Required for normal structure and integrity of adult vasculature (By similarity). Regulates the migration of vascular endothelial cells (PubMed:17540773). Required for normal extraembryonic angiogenesis and for embryonic heart development (PubMed:10625534). May regulate endothelial cell shape changes in response to blood flow, which drive vascular remodeling and establishment of normal vascular morphology during angiogenesis (PubMed:28530658). May play a role in the binding of endothelial cells to integrins. Acts as TGF-beta coreceptor and is involved in the TGF-beta/BMP signaling cascade that ultimately leads to the activation of SMAD transcription factors (PubMed:23300529). Required for GDF2/BMP9 signaling through SMAD1 in endothelial cells and modulates TGFB1 signaling through SMAD3 (By similarity). Homodimer; disulfide-linked (PubMed:8194490). Forms a heteromeric complex with the signaling receptors for transforming growth factor-beta: TGFBR1 and/or TGFBR2. Interacts with TGFB1 (PubMed:8194490). It is able to bind TGFB1 and TGFB2 with high affinity, but not TGFB3. Interacts with GDF2, forming a heterotetramer with a 2:2 stoichiometry. Interacts with ACVRL1. Can form a heteromeric complex with GDF2 and ACVRL1. Interacts with BMP10. Interacts with DYNLT4. Interacts with ARRB2. Detected on blood vessels (at protein level) (PubMed:8194490). Detected on adult pulmonary artery, capillaries supporting the heart muscle and lung alveolar capillary endothelial cells (PubMed:10625534). Endoglin is restricted to endothelial cells in all tissues except bone marrow and is also found in stromal cells within the connective tissue of intestine, stomach, heart, skeletal muscle, uterus, ovary, oviduct, testis and thymus (PubMed:8194490). Detected in embryo (at protein level). Detected in endothelium from yolk sac vessels. The ZP domain mediates dimerization. The N-terminal OR region is composed of two intertwined domains (OR1 and OR2) with a common, novel fold. Each contains 12 beta-strands that form a parallel beta-helix-like structure, plus a single alpha-helix. The OR1 region mediates interaction with GDF2. Full embryonic lethality at about 10.5 dpc. At 9.5 dpc, embryos display abnormal yolk sac vasculature and yolk sac anemia. Mutant embryos are also anemic, probably due to defective hematopoiesis in the yolk sac. In contrast, the embryonic vasculature appears grossly normal in most cases, but heart development is abnormal, and nearly all mutant embryos had enlarged ventricles and dilated outflow tracts. Besides, many had abnormal cardiac looping and displayed pericardial effusion. Heterozygous mice have occasionally abnormally convoluted and dilated blood vessels with disorganized smooth muscle cells surrounding them; these blood vessels are very fragile and rupture easily. Lacks a RGD motif, contrary to the human protein.