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 elutriat ion. Each fraction isolated mas examined by electron microscopy to elu cidate ultrastructural features consistent with differences in stages of cellular differentiation. As a rule, increasing cell size correlate d with evidence of progressive intracellular differentiation. This was represented by the appearance of specialization structures in later f ractions, and by changes in the density of organelles and other cellul ar constituents. Progressive development and maturation of the rough e ndoplasmic reticulum was also evident. These data are the first to dem onstrate successful subfractionation of the heterogeneous cytotrophobl ast cell population into distinct groups, each representing different levels of cellular differentiation. These morphologic features of diff erentiation correlate closely with established biochemical parameters associated with various stages of intermediate cytotrophoblast cell di fferentiation.