Loss of distinct arterial and venous boundaries in mice lacking endoglin, a vascular-specific TGFbeta coreceptor

Dev Biol. 2003 Sep 1;261(1):235-50. doi: 10.1016/s0012-1606(03)00158-1.


Several characteristic morphological and functional differences distinguish arteries from veins. It was thought that hemodynamic forces shaped these differences; however, increasing evidence suggests that morphogenetic programs play a central role in blood vessel differentiation. Hereditary hemorrhagic telangiectasia (HHT) is a vascular dysplasia characterized by the inappropriate fusion of arterioles with venules. The genes implicated in this disease, ALK1 and endoglin, may be involved in defining the fundamental boundaries between arteries and veins. We previously showed that mice lacking Alk1 lost structural, molecular, and functional distinctions between arteries and veins. Here, we report that mice lacking endoglin develop arterial-venous malformations and fail to confine intraembryonic hematopoiesis to arteries. In contrast to Alk1 mutants, endoglin mutants do not show profound vessel dilation or downregulation of arterial ephrinB2. Finally, our data indicate that a failure in cardiac cushion formation observed in both strains may be secondary to the peripheral vasculature defect. The phenotypic similarities, yet reduced severity, implicates endoglin as an accessory coreceptor that specifically modulates Alk1 signaling. We propose that endoglin and Alk1 are necessary for the maintenance of distinct arterial-venous vascular beds and that attenuation of the Alk1 signaling pathway is the precipitating event in the etiology of HHT.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Activin Receptors, Type I / deficiency
  • Activin Receptors, Type I / genetics
  • Activin Receptors, Type I / physiology*
  • Activin Receptors, Type II
  • Animals
  • Antigens, CD
  • Arteries / embryology
  • Arteriovenous Malformations / embryology
  • Arteriovenous Malformations / genetics
  • Base Sequence
  • Blood Vessels / embryology*
  • DNA / genetics
  • Endocardial Cushion Defects / embryology
  • Endocardial Cushion Defects / genetics
  • Endoglin
  • Ephrin-B2 / genetics
  • Hematopoiesis / genetics
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Phenotype
  • Receptors, Cell Surface
  • Receptors, Transforming Growth Factor beta / physiology*
  • Telangiectasia, Hereditary Hemorrhagic / embryology
  • Telangiectasia, Hereditary Hemorrhagic / genetics
  • Vascular Cell Adhesion Molecule-1 / genetics
  • Vascular Cell Adhesion Molecule-1 / physiology*
  • Veins / embryology


  • Antigens, CD
  • ENG protein, human
  • Endoglin
  • Ephrin-B2
  • Receptors, Cell Surface
  • Receptors, Transforming Growth Factor beta
  • Vascular Cell Adhesion Molecule-1
  • DNA
  • Activin Receptors, Type I
  • Activin Receptors, Type II
  • Acvrl1 protein, mouse