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Nuclear Envelope-Limited Chromatin Sheets (ELCS) form during excessive interphase nuclear envelope growth in a variety of cells. ELCS appear as extended sheets within the cytoplasm connecting distant nuclear lobes. Cross-section stained images of ELCS, viewed by transmission electron microscopy, resemble a sandwich of apposed nuclear envelopes separated by ~30 nm, containing a layer of ordered chromatin fibers. EM Procedures: The ultrastructure of ELCS was compared by three different methods: 1) aldehyde fixation/dehydration/plastic embedding/sectioning and staining; 2) high-pressure freezing/freeze substitution into plastic/sectioning and staining; 3) high-pressure freezing/cryo-sectioning/cryo-electron microscopy. Human leukemic (HL-60/S4) cells were treated with retinoic acid (4 days) to induce granulopoiesis, growth of nuclear envelope membranes, formation of lobulated nuclei and ELCS. Conclusions: ELCS exist in vivo; they are not an artifact of fixation. ELCS in ice are thicker than after dehydration and embedding in plastic. EM tomography of aldehyde fixed cells supports that the putative “30 nm fiber” in ELCS are composed of two overlapping layers of parallel “10 nm fibers”.

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Biochemistry, Biophysics, and Structural Biology | Cell and Developmental Biology


This poster won third-place in the Annual Diatome Award at the Microscopy Society of America's 2014 annual meeting, held August 3-7 in Hartford, CT.

ELCS In Ice: Cryo-electron Microscopy Of Nuclear Envelope Limited Chromatin Sheets



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