Fig. 5. Profile of the arrangement of rDNA in the nucleolus. (A) Although the FC contains large DNA clumps (arrows), FCs are still surrounded by decondensed rDNA; and the condensed DNA clumps within the FC are connected to rDNA fibers at the periphery of the FC. (B) Owing to different angles in sectioning, the periphery of some FCs (white arrows) is completely surrounded by rDNA, whereas in other FCs, the entire periphery is free of rDNA (black arrows). (C) After DNA staining, rDNA fibers were observed only at the DFC near the FC. The vacuoles of the nucleolus are mostly bleached, but their borders contain a few granular materials (white arrow). (D) rDNA is connected with the extranucleolar DNA at four sites (arrowheads). Bar, 0.5 µm.

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