Endoglin is expressed in the chicken vasculature and is involved in angiogenesis

Endoglin is a component of the transforming growth factor beta (TGF-beta) receptor complex, highly expressed by endothelial cells. Mutations in the endoglin gene are responsible for hereditary hemorrhagic telangiectasia type 1 (HHT1), an autosomal dominant vascular disorder caused by a haploinsufficiency mechanism. Vascular lesions (telangiectasia and arteriovenous malformations) in HHT1 are associated with loss of the capillary network, suggesting the involvement of endoglin in vascular repair processes. Using the chick chorioallantoic membrane (CAM) as an angiogenic model, we have analyzed the expression and function of chicken endoglin. A pan-specific polyclonal antibody (pAb) recognized chicken endoglin as demonstrated by immunostaining and Western blot analysis. In ovo treatment of chicken embryos with this pAb resulted in a significantly increased area of CAM. This effect was likely mediated by modulation of the ligand binding to endoglin as this pAb was able to inhibit TGF-beta1 binding. These results support the involvement of endoglin in the angiogenic process.