Figure 1. Isolated cytotrophoblast cells fuse and differentiate to form syncytiotrophoblast in vitro.

The cellular cytotrophoblast (CTB), a progenitor epithelium which regenerates the syncytiotrophoblast (SCT) continuously, can be isolated and cultured in vitro. The CTB then recapitulates developmental differentiation as it becomes SCT. Wheat germ agglutinin (magenta) was used to label plasma membrane; nuclei are labeled with Hoechst dye (blue). (1) At initial plating, CTB are round and contain numerous filopodial extensions. (2) By 24 h of culture CTB begin to aggregate and form intercellular contacts in preparation for fusion. (3) By 72 h in culture, virtually all isolated CTB have fused to form SCT. The regeneration of SCT from CTB in cultured placental explants follows a similar time course¹¹. Scale Bar: 5 μm.