Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 98, Issue 5, Pages 2399-2406Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.051631998
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Funding
- NCRR NIH HHS [RR 01229, RR 00592, P41 RR000592] Funding Source: Medline
- NIGMS NIH HHS [GM 42629, P01 GM61306, P01 GM061306, R01 GM042629] Funding Source: Medline
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The positional relationships among all of the visible organelles in a densely packed region of cytoplasm from an insulin secreting, cultured mammalian cell have been analyzed in three dimensions (3-D) at approximate to6 nm resolution. Pa rt of a fast frozen/freeze-substituted HIT-T15 cell that included a large portion of the Golgi ribbon was reconstructed in 3-D by electron tomography. The reconstructed Volume(3.1 x 3.2 x 1.2 mum(3)) allowed sites of interaction between organelles, and between microtubules and organellar membranes, to be accurately defined in 3-D and quantitatively analyzed by spatial density analyses. Our data confirm that the Golgi in an interphase mammalian cell is a single, ribbon-like organelle composed of stacks of flattened cisternae punctuated by openings of Various sizes [Rambourg, A., Clermont, Y., & Hermo, L. (1979) Am. J. Anat 154, 455-476]. The data also show that the endoplasmic reticulum (ER) is a single continuous compartment that forms close contacts with mitochondria, multiple trans Golgi cisternae, and compartments of the endo-lysosomal system. This ER traverses the Golgi ribbon from one side to the other via cisternal openings. Microtubules form close, non-random associations with the cis Golgi, the ER, and endo-lysosomal compartments. Despite the dense packing of organelles in this Golgi region, approximate to 66% of the reconstructed Volume is calculated to represent cytoplasmic matrix. We relate the intimacy of structural associations between organelles in the Golgi region, as quantified by spatial density analyses, to biochemical mechanisms for membrane trafficking and organellar communication in mammalian cells.
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