Three-dimensional structure of endosomes in BHK-21 cells.
Proceedings of the National Academy of Sciences of the United States of America
2899 - 2903.
The organization of the endosome compartment in BHK-21 cells was studied by using horseradish peroxidase as a fluid-phase marker and Semliki Forest virus as an adsorptive marker. Stereo pairs of semithin sections (0.2-0.5 μm) and computer-aided reconstruction and tracing of serial thin sections (CARTOS) were used to obtain three-dimensional images of the labeled compartments. Two types of labeled organelles could be observed: (i) small vesicles and tubules (~ 50 nm in diameter) and (ii) large complex structures consisting of central vesicular elements (with diameters up to 0.5 μm) and associated systems of radiating tubules. The large endosomes were located either in the peripheral cytoplasm or in the perinuclear region, and, importantly, they existed as independent organelles and not as an interconnected reticulum. Each endosomal vacuole had two to seven tubules oriented in random directions from the central vesicle. The tubules were 60-100 nm in diameter and up to 4 μm in length. Morphometric estimates indicated that 60-70% of the endosomal membrane was in the tubules, in contrast to 30-40% of the volume. No structural continuity between endosomes and Golgi cisternae was observed, although elements of the two systems were frequently found in close proximity.
|Title:||Three-dimensional structure of endosomes in BHK-21 cells|
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