Localization of endoglin, a transforming growth factor-beta binding protein, and of CD44 and integrins in placenta during the first trimester of pregnancy
Abstract
Endoglin is an integral membrane glycoprotein that binds transforming growth factor-beta 1 (TGF beta 1) with high affinity and is predominantly expressed on human endothelial cells. Characterization of this homodimeric protein from human term placenta has shown that it is particularly abundant on the syncytiotrophoblast. Immunofluorescence staining of sections of first trimester placenta now reveals that endoglin is found at even higher levels on the syncytiotrophoblast of samples ranging from 6 to 12 wk of gestation. Very low levels are observed on the undifferentiated cytotrophoblast cells that can be identified by their expression of the alpha 6 beta 4 integrin, a receptor for laminin. Within the villi, blood vessels and stromal cells are negative for endoglin but positive for alpha 1 beta 1 integrin, a receptor for collagens and laminin. Stromal cells also express CD44, a hyaluronic acid receptor. Of particular interest is the up-regulation of endoglin expression in the transition from polarized undifferentiated to non-polarized intermediate cytotrophoblasts (CTB) as the cells align in columns to invade the uterus. This occurs in parallel with the acquisition of alpha 5 beta 1 integrin (fibronectin receptor) and precedes th...Continue Reading
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