Distribution of fibrillar centers and silver-stained components in the nucleolus of human Sertoli cells.

The nucleolus of the human Sertoli cell consistently showed three distinct, spontaneously segregated parts: 1. one or two large, silver-positive fibrillar centers; 2. strands of dense fibrillar component continuous with the dense cords surrounding the fibrillar center. These components were also silver-positive; 3. a granular, silver-negative mass. These observations show that in the human Sertoli cell the number of fibrillar centers is far lower than the diploid number of NORs. They also suggest that the fibrillar center might contain several NORs in this cell type.