Uterine epithelial cells: Serving two masters.

Uterine epithelial cells are unique cells in that they are both epithelial in the typical barrier sense but in many mammalian species, they characteristically allow the blastocyst to penetrate them from the apical surface. Here we examine how these cells subserve both functions and in particular we synthesize recent evidence on focal adhesions and how these membrane structures contribute to uterine receptivity for blastocyst implantation. Focal adhesions emerge as a dynamic new player in the 'plasma membrane transformation' of early pregnancy and uterine receptivity in that they disassemble at the time of implantation in common with many other structures on the basolateral plasma membrane of these cells.