Ultrastructural characteristics of cytotrophoblast cells during stages of differentiation.

Isolated cytotrophoblast cells from term human placenta were separated into eleven fractions according to cell size, by centrifugal elutriation. Each fraction isolated was examined by electron microscopy to elucidate ultrastructural features consistent with differences in stages of cellular differentiation. As a rule, increasing cell size correlated with evidence of progressive intracellular differentiation. This was represented by the appearance of specialization structures in later fractions, and by changes in the density of organelles and other cellular constituents. Progressive development and maturation of the rough endoplasmic reticulum was also evident. These data are the first to demonstrate successful subfractionation of the heterogeneous cytotrophoblast cell population into distinct groups, each representing different levels of cellular differentiation. These morphologic features of differentiation correlate closely with established biochemical parameters associated with various stages of intermediate cytotrophoblast cell differentiation.