The expression of caveolin-1 and the distribution of caveolae in the murine placenta and yolk sac: parallels to the human placenta.

The expression pattern of caveolin-1 and the distribution of caveolae in the murine placental labyrinth and visceral yolk sac have been determined. Immunoblot analysis demonstrates that both placenta and yolk sac express the protein caveolin-1. Immunofluorescence microscopy was used to determine which cell types in the placental labyrinth and yolk sac express caveolin-1. In yolk sac, detectable caveolin-1 was restricted to endothelial cells and smooth muscle cells of the vitelline vasculature and to mesothelial cells. Endoderm, the major cell type in the yolk sac, does not express caveolin-1 as assessed by this assay. In the labyrinth region of the placenta, endothelial cells express caveolin-1 but this protein was not detectable in any of the three trophoblast layers. These tissues were also examined by electron microscopy to determine which cell types contain the specialized plasma membrane microdomains known as caveolae. Morphologically detectable caveolae were present in endothelial and smooth muscle cells, as well as mesothelial cells of the yolk sac and in endothelial cells of the placental labyrinth. Neither endodermal cells of the yolk sac nor trophoblastic cells in the placental labyrinth contained caveolae-like structures. We conclude that caveolin-1 and caveolae have restricted distribution in the murine placenta and yolk sac and that this parallels the situation in human placenta.