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Fig. 6. Hypertonic shock causes a complex pattern of segregation of nuclear compounds. (A) Upon in-vivo incubation of MCF7 cells with 320 mM sucrose medium and subsequent preparation for electron microscopy, ultrathin sections show chromatin (ch) as distinct portions of homogeneous, dense granularity. Lacunas of fine fibrillar material (fm) comprise a major fraction of the interchromatin space. They frequently include body-like structures of very low contrast and spherical shape (sb). Between chromatin and the fine-fibrillar lacunas, granular and fibrillar parts were arranged in various ultrastructural units, among them interchromatin granule clusters (ig), and dense bodies (db). At the nuclear periphery, the peripheral chromatin retracted by several hundred nanometers giving rise to the peripheral layer (double-headed arrow), which predominantly comprises fibrillar material like that of the interchromatin space. Its interface with the retracted chromatin is defined by several structures, among them small clusters of interchromatin granules (ig). The nucleolus (no) is of compact shape and homogeneous granular composition. Association with perinucleolar chromatin appears reduced. (B) Treatment with 160 mM sucrose medium caused intermediate states of nuclear re-organization. Although chromatin (ch) compacted to portions of similar texture, and dense bodies (db) arose as with 320 mM sucrose load, fine-fibrillar material (fm) did not segregate and separate from other nucleoplasmic compounds as sharply, e.g. interchromatin granule clusters (ig). Furthermore, peripheral and perinucleolar chromatin still associated with the nuclear envelope and the nucleolus (no), respectively. (C) Incubation of cells with 10% dextran of 41 kDa size had no influence on nuclear ultrastructure. Like control preparations, chromatin (ch) remained dispersed and did not cluster into distinct portions. Fine-fibrillar material did not segregate from interchromatin granule clusters (ig) and chromatin. The nucleolus (no) is of normal, polymorphous appearance, differentially organized into fibrillar and granular parts, and associated with perinucleolar chromatin. Bars, 1 µm.
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