To proliferate or to divide - to be or not to be

The authors investigate how cytotrophoblast (CTB) proliferation is coordinated with differentiation during early pregnancy, particularly focusing on the mechanisms that maintain a reservoir of CTB stem cells and regulate their exit from the cell cycle. They find that hypoxic conditions during the first trimester promote CTB proliferation, while differentiation and invasion are associated with down-regulation of mitotic markers and up-regulation of cell cycle inhibitors. Their results suggest that CTB proliferation and differentiation are part of a developmental program that is intricately timed with embryonic development.