Cloning and expression of a cDNA encoding mouse endoglin, an endothelial cell TGF-beta ligand

The rat monoclonal antibody, MJ7/18, which reacts selectively with the endothelium of blood vessels in mouse was used to screen a cDNA library derived from a transformed mouse brain endothelial cell line. The sequence of a cDNA encoding the cell surface MJ7/18 antigen revealed homology to human endoglin, a homodimeric transforming growth factor-beta (TGF-beta)-binding cell-surface glycoprotein expressed predominantly on vascular endothelial cells. Northern blot analysis shows a 3.4-kb single transcript of the mouse endoglin. The mouse endoglin is a type-I integral membrane protein of 653 amino acids (aa). The human and mouse sequences display 71% aa sequence identity with almost identical transmembrane and cytoplasmic domains. Like its human counterpart, mouse endoglin displays significant sequence homology to the type-III TGF-beta receptor in two extracellular domains, as well as striking similarity in the transmembrane and cytoplasmic regions. One of the extracellular regions of homology with TGF-beta receptor III represents a truncated version of a homology unit defining a novel gene family including uromodulin, the pancreatic granule protein gp2, and zona pellucida receptors for sperm. However, unlike its human counterpart, mouse endoglin does not contain an RGD tripeptide which has been suggested as a ligand of integrins.